<span>The student did not switch both instances of <span>x </span>with y. He should have written x = y2 + 12y.</span>He wrote only the principal square root instead of using the ± sign.<span><span>The domain is incorrect. For the radicand to be greater than or equal to zero, </span>x<span> must be less than or equal to zero. It should be </span>x <<span> 0.</span></span>
The first error was made when the variables were changed, the x in 12x was not changed to y. The second error was when the square root of -11x was taken, for -11x to be positive x should be less than 0 not greater or equal to 0.
