1)сosx<0⇒x∈(π/2+2πn,3π/2+2πn)
-cosx=cosx-2sinx
2sinx-2cosx=0/cosx
2tgx-2=0
tgx=1
x=π/4+πn +x∈(π/2+2πn,3π/2+2πn)
х=5π/4+2πn,n∈z
2)cosx≥0⇒x∈[-π/2+2πn;π/2+2πn,n∈z]
cosx=cosx-2sinx
sinx=0
x=πn +x∈[-π/2+2πn;π/2+2πn,n∈z]
x=2πn,n∈z
3x+6+x+1<span><12+4x
3x+x-4x<12-6-1
0<5
</span>
-(0.4)^2=-0.16
1.4-10/7=7/5-10/7=49/35-50/35=-1/35
-0.16/-1/35=16/100*35=28/5=5.6