11/x-9=-10
11-9x=-10x
-9x+10x=-11
x=-11
cos^-1(2x^2-1)=cos^-1(3x+1)
2x^2-1=3x+1
2x^2-3x-2=0
x-2=0 и 2x+1=0
x=2 и x=-1/2