Question

The sumof the angle measures of any triangle is 180 degrees. Suppose that one angle in a triangle has a degree for 6x-9 and another has a degree measures 9x+1. Write an expression for the degree measure of the third angle in the triangle.

Answer 1

Remark
No matter what kind of triangle it is, the angles must add up to 180, just as you said.

Suppose we say 
A = 6x - 9
B = 9x + 1
C = y          We need an expression for C or y.

A + B + C = 180
6x - 9 + 9x + 1 + y = 180   Collect the like terms on the left.
6x + 9x + 1 - 9 + y = 180
15x - 8 + y = 180               Add 8 to both sides.
15x + y = 180 + 8
15x + y = 188                    Subtract 15x from both sides.
y = 188 - 15x <<<<<<<<< Answer