3cos^2x + 5cosx =0

Answer 1

3cos²x +5cosx=0

cosx(3cosx+5)=0

cosx=0 and cosx =-5/3

for cosx=0 the general solution is given by ±π/2+2kπ

and for cox=-5/3 the general solution is given by ±cos^-1(-5/3)+2kπ

where k is integer

Answer 2

Factor out cosx and then set each factor to 0

OR, let u=cosx and get 3u^2 + 5u =0. Then factor out u.