Question

$4sin^{2} x -11 cosx +10 cos^{2} x=0$

Answer 1

4sin²x-11cosx+10cos²x=0
4-4cos²x-11cosx+10cos²x=0
6cos²x-11cosx+4=0
cosx=a
6a²-11a+4=0
D=121-96=25
a1=(11-5)/12=1/2⇒cosx=1/2⇒x=+-π/3+2πn
a2=(11+5)/12=4/3⇒cosx=4/3>1 нет решения