Question

Решить уравнение:
1) 4cos^2 x+cos x-5=0
2) (2:3)^8x+1=1,5^2x-3

Answer 1

[tex]1) 4 cos ^{2} x+cosx-5=0 \ cosx=t \ 4 t^{2} +t-5=0 \ D=1+80=81 \ sqrt{D} =9 \ x_{1} = frac{-1+9}{8} =1 \ x_{2} = frac{-1-9}{8} =-1.25 \ cosx=-1.25 \ -1