this post was submitted on 08 Oct 2024
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[–] Brosplosion@lemm.ee 56 points 3 days ago (3 children)

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

[–] Leate_Wonceslace@lemmy.dbzer0.com 26 points 3 days ago (1 children)

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

[–] PresidentCamacho@lemm.ee 14 points 3 days ago (1 children)

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

[–] myusernameis@lemmy.ca 7 points 3 days ago

Random woman who didn't sleep very well last night. I got a different answer, then thought about it for 10 more seconds and then got 135.

(No I didn't assume the right angle, my mistake was even dumber. I need a nap.)

[–] TheOakTree@lemm.ee 13 points 3 days ago (1 children)

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.

[–] NoMoreLurkingToo@startrek.website 22 points 3 days ago (3 children)

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.

[–] Windex007@lemmy.world 0 points 3 days ago

which would make the calculation of x literally impossible

Yes.

But that doesn't mean that line must be straight. It just means if it isn't, you can't derive x.

[–] TheOakTree@lemm.ee -5 points 3 days ago* (last edited 3 days ago) (2 children)

You're overlooking a major assumption on your end. There is nothing in the image that suggests that the bottom of both triangles forms a straight line. The pair of bottom edges are two separate lines. They may or may not form a sum 180° angle. You are assuming the angles are supplementary. We know that the scale of the image is wrong, thus it is not safe to definitively say that the 80° angle's neighbor is supplementary. They may be supplementary, or the triangles may share a consistently skewed scale, or the triangles may each have separately skewed scales.

This is a basic logical thought process and basic trigonometry.

[–] Leate_Wonceslace@lemmy.dbzer0.com 20 points 3 days ago (1 children)

There is nothing in the image that suggests that the bottom of both triangles forms a straight line.

Except for the part where it's a single straight line segment, as depicted in the image. Showing the complimentary angles as an unlabeled approximately right angle is within convention. Showing a pair of line segments that do not form a straight line as a straight line is not.

Exactly.

Add to this that x is literally impossible to calculate if conventions are not assumed, and absolutely possible to calculate if conventions are followed. Assuming the conventions won't hold is an irrational position.

[–] NoMoreLurkingToo@startrek.website 19 points 3 days ago (2 children)

What you say makes no sense.

The problem is LITERALLY unsolvable if we can't assume that all the lines are straight.

The schematic was OF COURSE purposefully drawn in a way to make the viewer assume that the third angle of the left triangle is 90°, making the angle to it's right also be 90°, but the point of the exercise is to get the student to use ALL the given information instead of presuming right angles.

And NO, assuming all the lines are straight is NOT unreasonable, it is the only way that the problem could ever possibly have a solution.

[–] jj4211@lemmy.world -2 points 2 days ago

I'd say that the shape on the left has what appears to be a little kink right near X, so one might infer that the shape on the left might be a quadrilateral. There are blatantly obvious vertices that are not labeled as such, so we can't assume that the not-quite-straight line is supposed to be straight since other angles are also not explicitly indicated as vertices...

[–] Siethron@lemmy.world 1 points 2 days ago

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.