Question

Prove that cos20degree cos 40degree cos60degree cos80degree=1/16

Answer 1

Answer:

cosx×cos(60∘−x)×cos(x+60∘)=cos3x4

cos(20∘)cos(40∘)cos(60∘)cos(80∘)

=cos(20∘)cos(40∘)cos(80∘)cos(60∘)

=cos(20∘)cos(60∘−20∘)cos(60∘+20∘)cos(60∘)

=cos(60∘)4×12

=12×4×12

=116

Step-by-step explanation:

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