Я решил, вроде равно нуль
y = - (x^2+36)/x
y= -(x+36/x)=-x-36/x
y'=-1+36/x^2
-1+36/x^2=0
1-36/x^2=0
(x^2-36)/x^2=0
(x-6)(x+6)/x^2=0
x=-6;x=6;x=0
- + + -
-----(-6)------(0)-----(6)----->x => x=6 - точка максимума
V ^ ^ V
2) cosx-√3sinx=√2 |:2
½cosx-√3/2sinx=√2/2
½=sin(π/6); √3/2=cos(π/6)
sin(π/6)cosx-cos(π/6)sinx=√2/2
sin(x-π/6)=-√2/2
x-π/6=(-1)^n•arcsin(-√2/2)+ πn
x-π/6=(-1)^(n+1)•arcsin(√2/2)+ πn
x=(-1)^(n+1)•π/4+π/6+ πn