9/72
I forgot how to do this
When

, you have

Now assume this is true for

, i.e.

and under this hypothesis show that it's also true for

. You have




In other words, there exists

such that

Rewriting, you have



and this is equivalent to

modulo 9, as desired.
Answer:
The triangle is obtuse.
It is an isosceles triangle.
The angles add up to 180°.
Step-by-step explanation:
Obtuse triangles are defined as triangles with one angle obtuse angle over 90°. This triangle has an angle of 100°, so it is an obtuse triangle!
Isosceles triangles have 2 equal sides. The two orange dashes on the left and right legs of the triangle tell us they are equivalent, so this is an isosceles triangle as well!
Finally, <em>all </em>triangles add up to 180°! We can prove this by adding the angles.
40° + 40° = 80°
100° + 80° = 180°