Question

If sin 18${}^{\circ }$ =$\frac{\sqrt{5}-1}{4},$ then sin 81${}^{\circ }$ is equal to

• A. $\frac{\sqrt{5}+1}{4},$
• B. $\frac{\sqrt{3+\sqrt{5}}+\sqrt{5-\sqrt{5}}}{4}$
• C. $\frac{\sqrt{10+2\sqrt{5}}}{4}$
• D. none of these.

Answer 1

Answer: (B)

Correct answer is (b) $\frac{\sqrt{3+\sqrt{5}}+\sqrt{5-\sqrt{5}}}{4}$