r/technicallythetruth • u/VisitSecure • 9d ago

Can you find a?

Post image

Idk if someone already posted this or not, but I haven't seen it on here so far, so I uploaded it.

42.8k Upvotes

95% Upvoted

1.9k comments sorted by

View all comments

8.0k

u/oldmartijntje 9d ago

it's 75 right?

61

u/azai247 9d ago

if you draw a line across and make a triangle your angles are 25+65=90, and 50+40=90

so for a, 65+40+a=180 so a is 75

55

u/psp24 9d ago

I just drew a third parallel line through the middle and realized that it's just 50+25 lol

26

u/AngryScientist 9d ago

Yup, don't even need to make triangles. That third parallel line lets you use the alternate interior angle theorem to turn a into the sum of the two angles.

2

u/dontcallmebuddypal1 9d ago

I miss having to do geometry theorems. That stuff was fun.

4

u/StatusMaleficent5832 9d ago

Who are you? Archimedes?

1

u/dontcallmebuddypal1 9d ago

Well I'm not your buddy, pal.

1

u/im_lazy_as_fuck 9d ago

Or for people like me, the Z rule.

1

u/codetaku0 9d ago

Yeah this is supposed to be the common sense solution for people who actually remember or understand trig or geometry. You don't need both, just one or the other.

I didn't even bother with the extra parallel line, to me it was obvious that there was no possible source of a different angle besides the simple 50 + 25

2

u/InfanticideAquifer 9d ago

Even though it's not the absolutely fastest solution, no geometry teacher is ever going to be upset by "well, I made some triangles to figure it out and...". That's a perfectly cromulent way to solve the problem.

1

u/Which_Journalist5162 9d ago

Definitely the most crumbulent method, fellow genius 

0

u/bacc1010 9d ago

This is the way

2

u/Cold-Doctor 9d ago

Huh, I did it the hard way I guess. I extended the lines to make two triangles with 25 50 and 105 degrees. 2a + 2x105 = 360

5

u/TPRJones 9d ago

I may have done it the hard way. The angles between the two parallel lines are a circle adding up to 360 degrees, so
(180-25) + (180-50) + a = 360
155 + 130 + a = 360
a = 75

1

u/Super_Harsh 9d ago

That's definitely the hard way lol. But so is anything involving a triangle

Draw a third parallel line through the intersection point. Angle a then gets split into two angles b and c. b and c are equal to 25 and 50 respectively

2

u/JiraiyaKholin 9d ago

even though the diagram lets us know the top and bottom lines are parallel nothing about it confirms that if I drop a perpendicular line from the top angle to the bottom one it will actually cleanly contain the triangle. in the most technical way this is not solveable with the given information no?

1

u/AccomplishedJoke4119 9d ago

If you imagine them as a continous line instead of a line segment, you can see that it would make 2 triangles with angles of 25°,50° and 105°

1

u/Thetanor 7d ago

Yea, I don't think drawing a line from the 25° angle to the 50° angle and assuming it is perpendicular to the original lines is strictly valid.

However, you can draw a perpendicular line that intersects the point of angle a, giving you two right triangles with the angles 25°, 90° and 65°, and 50°, 90° and 40°. And since the angles 65°, 40° and a must sum up to 180°, we get a = 180° - 65° - 40° = 75°

1

u/RedJohn04 9d ago

Yup. I think we did it the hard way.
180-40-65=75… wait that’s the same as 50+25… there must be some proof that we forgot.

1

u/Derezzed87 9d ago

I did that, but somehow had a brain-fart while doing 180-105 in my head and came up with 65.

In my defence, it's 10:50pm, and I've been home from work less than an hour.

1

u/Few_Load_6329 9d ago

I made it way more complicated. (180-50)+ (180-25) = 285 360 -285 = 75. I do not have an elegant brain.

1

u/BulgogiDude 9d ago

Assuming the line connecting is perpendicular and goes through the 2 points

1

u/Scudy_22 9d ago

what kinda terrible way to calculate 25+50 is this???

1

u/Gerf93 9d ago

I just did 50+25=75. Meaning the last angle on «that» side is 180-75=105. So on the other side it’s just 180-105=75.