7
4x²+23x-6≤0
D=529+96=625
x1=(-23-25)/8=-6 U x2=(-23+25)/8=1/4
x∈[-6;1/4]
8
cos²a/(sina+1)=(1-sin²a)/(sina+1)=(1-sina)(1+sina)/(sina+1)=1-sina
9
sin2x=-1
2x=-π/2+2πk
x=-π/4+πk,k∈z
4
y=-x³+9x
y`=-3x²+9
-3(x²-3)=0
x²=3
x=-√3 U x=√3
_ + _
------------------(-√3)---------(√3)-------------------
min max