Answer:
see explanation
Step-by-step explanation:
Using the double angle identity for sine
sin2x = 2sinxcosx
Consider left side
cos20°cos40°cos80°
= [tex]\frac{1}{2sin20}[/tex] (2sin20°cos20°)cos40°cos80°
= [tex]\frac{1}{4sin20}[/tex] (2sin40°cos40°)cos80°
= [tex]\frac{1}{4sin20}[/tex] (sin80°cos80° )
= [tex]\frac{1}{8sin20}[/tex] (2sin80°cos80° )
= [tex]\frac{1}{8sin20}[/tex] . sin160°
= [tex]\frac{1}{8sin20}[/tex] . sin(180 - 20)°
= [tex]\frac{1}{8sin20}[/tex] . sin20°
= [tex]\frac{1}{8}[/tex] = right side , thus proven
