Question

Решите уравнение 2cos^2x+3cosx=0

Answer 1

2cos^2x -3cosx=0
2(1-sin^2x)-3cosx=0
2-2cos^2x-3cosx+=0
-2cos^2x-3cosx+2=0
2cos^2x+3xcos-2=0
D=9-4(-2*2)=9+16=25

cosx1=(-3+5)/4=2/4=1/2

cos2=(-3-5)/4=-8/4=-2 
x=1/2
x=(-1)^m*п/6+пm, m э z.