1) 7sin^2x-4sin2x+cos^2x=0

2) sin^2x-3sinx*cosx+2cos^2x=0

Ответы:

22cos^2x+4(2sinxcosx)=7(cos^2x+sin^2x)

22cos^2x+8sinxcosx=7cos^2x+7sin^2x

15cos^2x+8sinxcosx-7sin^2=0          /:cos^2

15+8tgx-7tg^2x=0

tgx=t

-7t^2+8t+15=0

7t^2-8t-15=0

D=64+420=484

t=8(+-)22

14t1=2

t2=1

tgx=1       tgx=2

x=arctg1+ПK    x=arctg2+ПK