Do you mean square root of(11-x) ?
If so, [square root(11-x)]^2=(x+1)^2
11-x=x^2+2x+1
11=x^2+3x+1
0=x^2+3x-10
x^2+3x-10=0
(x+5)(x-2)=0
x+5=0, x=-5
x-2=0, x=2
check: SQRT(11-(-5))=SQRT(16)=4 and x+1=-5+1=-4 but SQRT symbol means principal root
(the nonnegative root)
we don't use -5 as a solution
SQRT(11-2)=SQRT(9)=3 and x+1=2+1=3
we use x=2 as a solution
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