Question

4cos^2(x)+sin(x)-1=0

Answer 1

4cos²x+sinx-1=0
4-4sin²x+sinx-1=0
4sin²x-sinx-3=0
sinx=1, sinx=-$\frac{3}{4}$
x=$\frac{ \pi }{2}$+2πn, n∈Z или x=$(-1)^{n+1}$arcsin$\frac{3}{4}$+πm, m∈Z