Quote by cstvlr
no its in an equation form,
C(x) = [(9x) + 1.25sqrt( x^2 + 36 )], where C(x) is a function.
and they're trying to solve for x, so they used the method above, and I know how to solve it, but I lost it when they used let x = 3( t  1/t )

x = 3( t  1/t ) ⇒ x
^{2} = 9( t  1/t )
^{2}
∴√(36+x
^{2})=√(36+9(t 1/t)
^{2}), how does that turn into an expression like √(a+b)
^{2}?
I do not think there rule per se for using that substitution though.