Question 923911
<img src="http://upload.wikimedia.org/wikipedia/commons/thumb/7/7e/Trigonometry_triangle.svg/200px-Trigonometry_triangle.svg.png ">
think of half of the Isosceles triangle: 
Per Diagram:
b = (1/2)Base = 15cm  and h = 17 sm
&#8736;A = cos(A) = 15/17
&#8736;A = 28°  Using Calculator