Question 470569
{{{sqrt(x) = 42 - x}}}
==> {{{x = (42 - x)^2}}} <==> {{{x = 1764 - 84x + x^2}}}

==> {{{X^2 - 85x + 1764 = 0}}} ==> (x - 36)(x - 49) = 0

==> x = 36, x = 49.

Eliminate the second x-value, because it doesn't satisfy the original equation.

x = 36 satisfies the original equation.  Hence it is the final answer.