Question

cos20 degre*cos40*cos60*

Answer 1

Conditions

cos20 degre*cos40*cos60*

Solution

$$\begin{array}{l} \cos 20{}^\circ \cos 40{}^\circ \cos 60{}^\circ = \frac{\cos(40{}^\circ - 20{}^\circ) + \cos(40{}^\circ + 20{}^\circ)}{2} \cos 60{}^\circ = \frac{\cos 20{}^\circ + \frac{1}{2}}{2} \cdot \frac{1}{2} = \frac{\cos 20{}^\circ}{4} + \frac{1}{8} \\ \approx 0.355923155 \end{array}$$