An isosceles triangle has two congruent sides of length 15 i

An isosceles triangle has two congruent sides of length 15 inches. The remaining side has a length of a inches. Find the angle that a side of 15 inches makes with the 8 inch side The line y - 7/8 x passes through the origin in the xy plane. What is the measure of the angle that the line makes with the positive x axis?

Solution

Apply cosine rule :

c^2 = a^2 + b^2 -2abcosA

cosA = ( a^2 + b^2 - c^2)/2ab

= ( 15^2 + 8^2 - 15^2)/2*15*8

= 0.267

A = 74.534 deg = 1.30 radians