A plot of land in the shape of a quadrilateral is enclosed by a fence. One side of fence measures 78 feet and an adjacent side of fence measures 135 feet. The diagonal of the quadrilateral forming a triangle with these two sides measures 174 feet.
What is the measure of the angle between the two sides of fencing?
I would use cosin rule
c^2 = a^2 + b^2 - 2ab cos c
174^2 = 78^2 + 135^2 - 2 (78)(135) cos c solve for cos c then find angle measure c via arc cos