Задача 2687 2cos^2x - cos x -1 =0 ...

dedok9

14.01.2015

2cos^2x - cos x -1 =0

slava191

14.01.2015

Cosx=t
2t^2-t-1=0
D=1+4*2=9
.t1=1+3/4=1 t2=1-3/4=-1/2
Cosx=1
X=2Pin
Cosx=-1/2
X=+/-2Pi/3+2Pin