Given that (theta) is an acute angle and sin (theta) = (frac{m}{n}), find cos (theta)

A.
(frac{sqrt{n^2 – m^2}}{m}) 
B.
(frac{sqrt{(n + m)(n – m)}}{n}) 
C.
(frac{m}{sqrt{n^2 – m^2}}) 
D.
(sqrt{frac{n}{n^2 – m^2}})
Correct Answer: Option B
Explanation
sin (theta) = (frac{m}{n})
Opp = m; Hyp = n
Adj = (sqrt{n^{2} – m^{2}})
(cos theta = frac{sqrt{n^{2} – m^{2}}}{n})
= (frac{sqrt{(n + m)(n – m)}}{n})