Question 11528
x/sqrt.(x^2 +7 )  = y

squaring on both sides, we have:

x^2
__________   =  y^2  therefore
x^2  +  7

x^2  =  x^2*y^2  + 7y^2  or

x^2  -  x^2y^2  =  7y^2  or

x^2(1 -y^2)  =  7y^2  or

x^2  =  7y^2 / 1 - y^2  or

x  =  sqrt.( 7y^2 / 1-y^2 )  ans.