Question

What is the value of y?

Answer 1

The little tic marks on each of the triangle's sides are there to tell you that the sides are all equal, and therefore, yes, it is an equilateral triangle.

Since all the sides are equal, a geometry theorem tells us that all the angles are equal.

You may try to set the two expressions for the two angles equal to each other, but you will still be stuck.

Since all three angles are equal, and since there are a total of 180 degrees in a triangle, each angle has to be 60 degrees.

So to find y, set the expression for angle A equal to 60 and solve for y.

60 = 5y + 10
50 = 5y
10 = y

y = 10