prove that.470casosTot ce en74 ca

1.	prove that.470casosTot ce en74 ca
Answer» cos^2 pi/10 + cos^2 3pi/10 + cos^2 6pi/10 + cos^2 8pi/10 = cos^2 pi/10 + cos^2 3pi/10 + cos^2 3pi/5 + cos^2 84pi/5 = cos^2 pi/10 + cos^2 3pi/10 + sin^2 (pi/2 - 3pi/5) + sin^2(pi/2 - 4pi/5) = cos^2 pi/10 + cos^2 3pi/10 + sin^2 (-pi/10) + sin^2(-3pi/10) = (cos^2 pi/10 + sin^2 pi/10) + cos^2 (3pi/10) + sin^2 (3pi/10) = 1 + 1 = 2

Answer»

cos^2 pi/10 + cos^2 3pi/10 + cos^2 6pi/10 + cos^2 8pi/10

= cos^2 pi/10 + cos^2 3pi/10 + cos^2 3pi/5 + cos^2 84pi/5

= cos^2 pi/10 + cos^2 3pi/10 + sin^2 (pi/2 - 3pi/5) + sin^2(pi/2 - 4pi/5)

= cos^2 pi/10 + cos^2 3pi/10 + sin^2 (-pi/10) + sin^2(-3pi/10)

= (cos^2 pi/10 + sin^2 pi/10) + cos^2 (3pi/10) + sin^2 (3pi/10)

= 1 + 1

= 2

Discussion