Question

If sinA + cosecA = 2 (where 0°< A < 180°) then find-
(i) cos³A + 3cos A =

Answer 1

If A =30°

cos3A=Acos 3 A−3cosA

cos90 ∘ =4(cos30 ° )2 −3(cosA30 ∘ )

0=4.(√3/2)= 3.√3/2

0=(4.√3/2x2x2)-(3√3/2)

0=(3√3/2)-(3√3/2)

0 =0

LHS = RHS