150 баллов! Тригонометрия

sin^2x+2cos^x=sin^2x+cos^2x+cos^2x=1+cos^2x
0<=cos^2x<=1
1<=1+COS^2X<=2
1+2=3
3cos^2x-4sin^2x=3cos^2x-3sin^2x-sin^2x=3cos2x-sin^2x
-1<=-sin^2x<=0
-3<=3cos2x<=3
-4<=3cos2x-sin^2x<=3
-4+3=-1