\[cosA cos (60+A)cos (60+A)=\frac{1}{4}cos 3A\]
LHS=\[cosA cos (60+A)cos (60+A)\]
=\[cosA cos^260-sin^2 A\]
=\[cosA ( \frac{1}{4}-sin^2 A)\]
=\[cosA ( \frac{1}{4}-(1-sin^2 A))\]
=\[\frac{1}{4}(4cos^3(A)-3sinA))\]
=\[\frac{1}{4}cos3A\]
For A=20 we get 0.125
