PQRS is a rhombus of side 16cm. The diagonal QS = 20cm. Calculate, correct to the nearest degree, ∠PQR

A.
51^{o} 
B.
64^{o} 
C.
77^{o} 
D.
103^{o}
Correct Answer: Option D
Explanation
cos(alpha) = (frac{10}{16}) = 0.625
(alpha) = cos^{1}(0.625)
= 51.3^{o}
∠PQR = 2(alpha)
= 2(51.3^{o})
= 102.6
= 103^{o}