62 points

All these people saying its 135 are making big assumptions that I think is incorrect. There’s one triangle (the left one) that has the angles 40, 60, 80. The 80 degrees is calculated based on the other angles. What’s very important is the fact that these triangles appear to have a shared 90 degree corner, but that is not the case based on what we just calculated. This means the image is not to scale and we must not make any visual assumptions. So that means we can’t figure out the angles of the right triangle since we only have information of 1 angle (the other can’t be figured out since we can’t assume its actually aligned at the bottom since the graph is now obviously not to scale).

Someone correct me if I’m wrong.

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7 points

Stupid stuff like this is why kids hate math class. Unless the problem says calculate all unmarked angles, those visually 90 degree angles are 90 degrees. It works that way in any non engineering job that uses angles because it’s common sense.

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15 points
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…what? I get that this drawing is very dysfunctional, but are you going to argue that a triangle within a plane can have a sum of angles of 190°?

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15 points

Nope I’m not saying that. I’m saying this is a gotcha question that demotivates learners.

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0 points

No, they’re saying that unless you’re already good at this stuff, it’s easy to assume that a visually 90° angle is actually 90° even when it’s not

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2 points

The sum of the angles of a triangle are always 180°

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56 points

135 is correct. Bottom intersection is 80/100, 180-35-100 = 45 for the top of the second triangle. 180 - 45 = 135

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13 points

You’re making the assumption that the straight line consisting of the bottom edge of both triangles is made of supplementary angles. This is not defined due to the nature of the image not being to scale.

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22 points

Unless there are lines that are not straight in the image (which would make the calculation of x literally impossible), the third angle of the triangle in the left has to be 80°, making the angle to its right to be 100°, making the angle above it to be 45°, making the angle above it to be 135°. This is basic trigonometry.

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1 point

When you’re finding the outside angle along the line of a triangle you don’t need the inside angle tied to that outside angle if you have the other two inside angles since both straight lines and triangles total to 180 degrees.

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26 points

Mathematician here; I second this as a valid answer. (It’s what I got as well.)

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14 points

Random guy who didn’t sleep in middle school here: I also got the same answer.

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0 points

Your assumption is that it’s a Cartesian coordinate system with 90° angles. But that’s not necessarily the case. You can apply a sheer transformation to correct for the unusual appearance. When you do that, the angles change, but straight lines stay straight and parallels stay parallel. There’s a mathematical term for that, which I can’t remember right now.

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21 points

I mean, the assumption shouldn’t be anything about scale. It should be that we’re looking at straight lines. And if we can’t assume that, then what are we even doing.

But, assuming straight lines, given straight lines you find the other side of an intersecting line because of complements.

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2 points
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We can’t assume that the straight line across the bottom is a straight line because the angles in the drawing are not to scale. Who’s to say that the “right angle” of the right side triangle isn’t 144°?

If the scale is not consistent with euclidian planar geometry, one could argue that the scale is consistent within itself, thus the right triangle’s “right angle” might also be 80°, which is not a supplement to the known 80° angle.

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4 points

And if we can’t assume that, then what are we even doing

That’s exactly what the other user is saying. We can’t assume straight lines because the given angles don’t make any sense and thus this graph is literally impossible to make. We’re arguing over literal click bait is what we’re doing.

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16 points

Why do the labeled angles prevent us from assuming straight lines?

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1 point

thx for the compliment

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7 points

I’d argue that the bottom line is indeed one continuous line regardless of how many other lines intersect on it, because there’s nothing indicating that the line is broken at the intersection.

Now the only reason I think the lines are straight at all is use of the angular notations at the ends, which would be horribly misleading to put at the end of curves or broken lines.

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3 points

You’re making the assumption that they are triangles.

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39 points

This is a standard way to draw geometric proofs, it’s not at all unreasonable to assume straight lines alongside unrepresentative angles. It’s certainly still an assumption, but a conventional one.

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-2 points
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For the love of dog, you can’t solve this problem without making assumptions that fundamentally change the answer. People are too quick to spot the first error and then make assumptions that are conveniently consistent with the correction.

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10 points
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The only assumption needed to solve the problem is that the bottom line is indeed straight. Generally it will never be assumed in these types of learning practices that a straight line is a lie, because at that point you can never do a single problem ever. However an undefined angle can be cheesed.

Though it still bugs me on a fundamental level they will cheese the angle to bait a person into a wrong answer, it can teach a valuable lesson about verifying information.

We can solve this issue of a straight line being guaranteed by doing this. This actually is probably a really good practice considering the exacting nature of certain disabilities such as ADHD and Autism. However if you live in the US you need to just accept things like this because we will NEVER fund public education properly let alone consider accessibility beyond things mandated by the ADA

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11 points

The answer is 125 degrees but the triangle on the left has 190 degrees in it

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5 points
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Nah, the angle isn’t specified as a right angle. We can’t assume it’s 90° just because it’s drawn that way, because it isn’t drawn to scale.

Left triangle has 180° total. 60+40=100, which means that middle line is actually 80°, not 90. And since the opposite side is the inverse, we know it is 100° on the other side.

100+35=135. We know the right triangle also has 180° total, so to find the top corner we do 180-135=45. So that top corner of the right triangle is 45°, meaning x must be 135° on the opposite side.

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0 points

I mean, it’s visibly an acute angle wether it’s labelled as such or not.

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10 points
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125°

Edit: Damn I’m getting roasted for getting it wrong. I totally am wrong, but when I’ve been awake for only 5 minutes that’s bound to happen XD

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0 points

This guy angles

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9 points

He actually doesn’t lol. It’s 135°.

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8 points

Nah he definitely does angle. Maybe not super well or anything but there’s clearly some angling happening

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21 points
Removed by mod
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7 points

Or 135°

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8 points

It’s a trap. The drawing is misleading. If the left triangle already has 60° and 40° then only 80° remains. Meaning there’s no right angle. The vertical line should be leaning to the left slightly. The correct answer is 135°.

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5 points

Good on you for admitting fault, not deleting the post, and standing strong. I know you probably feel like a total braindead fucking moron right now - and you’d be right to - which may be the only thing you’ve gotten right in your whole life. /s

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2 points

Not to scale. Left triangle shows that the centre tee is actually 80/100⁰, not two right angles. So right triangle is 100+35+45, angle x is 135⁰.

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3 points

5/10 show your work next time! /s

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7 points

Wrong, as the drawing is not representative. The inner lower angle for the right triangle has to be 100°, as such the inner upper angle has to be 45° and the X angle has to be 135°.

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8 points

Federation in action: 5 different people from 4 different instances correct OP, not knowing the others have done so, because federating the answers takes a minute.

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2 points

To be fair I wrote the answer, then figured “surely somebody else must’ve written an answer by now”, refreshed, saw two other answers (one 12 seconds old), thought “fuck it” and posted anyway. They’re all written a bit differently so maybe some are easier to understand than others.

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2 points

I think 125

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24 points

135, that’s not a 90 degree angle in the problem. Just visually.

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7 points

Oh that’s just a cheap trick. You are right, it’s 80 degrees despite looking like 90 degrees.

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1 point

You are right that is 80° so the value of x will be 135°

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8 points
*

Nah, the imagery tricks you. 180 degrees to a line. 180 degrees inside a triangle.

So you can gather the inside unlabeled angle on the triangle on the left is only 80 degrees: (180-[60+40])

So you then know it’s 100 on the right side of that +35 leaves you with 45 degrees left for the top of the right one.

180-45=. 135 degrees

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6 points

Also if you add up all visible angles you get 135, so I’m sold on that alone. No no no, I won’t hear any rebuttals.

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