Question

8cos³20°-8sine³10°-6cos20°+6sin10°=2

Answer 1

Step-by-step explanation:

L.H.S.

= 8cos320 – 8sin310 – 6cos20 + 6sin10

= 2(4cos320 – 4sinn310 – 3cos20 + 3sin10)

= 2(4cos320 - 3cos20 + 3sin10 – 4sin310)

= 2(cos3.20 + sin3.10) [∵ cos3A = 4cos3A – 3cosA and sin3A = 3sinA – 4sin3A]

= 2(cos60 + sin30)

= 2(1/2 + 1/2)

= 2