Answer:
see explanation
Step-by-step explanation:
Using the double angle identity
sin2x = 2sinxcosx
Consider the left side
cos20. cos40. cos80
= [tex]\frac{1}{2sin20}[/tex] (2sin20cos20)cos40.cos80
= [tex]\frac{1}{2sin20}[/tex] (sin40cos40cos80
= [tex]\frac{1}{4sin20}[/tex] (2sin40cos40)cos80
= [tex]\frac{1}{4sin20}[/tex] (sin80cos80)
= [tex]\frac{1}{8sin20}[/tex] (2sin80cos80)
= [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]
Hence
8(cos20cos40cos80) = 8 ×[tex]\frac{1}{8}[/tex] = 1 = right side
