What is the coefficient of the term x7y in the expansion of (x + y)^8? a1 b8 c28 d56,

the sum of all the angles in a triangle are equal to 180

so you can add   the 3 given angles together to equal 180:

5y + 2y + 2y = 180

or since all three angles have the same letter, combine the 3 angles to equal 180:

9y = 180