Question

cos^2 3π/5+cos^2 4π/5

Answer 1

Answer:

Cos^2 108 + Cos^2 144

»»» Cos ^2 (90+18) + Cos^2( 90+54)

»»» Sin^2 18 + Sin^2 54

We know that,

Sin 18 is equals to root over 5 minus 1 divided by 4.,, √5 - 1 /4 and sin 54 = √5+1/4

(√5 - 1/4 )^2 + (√5+1/4)^2

= 4/16+6/16

:-):-)