Predict the result
For the square root of x plus two equals x, do two and negative one work?
Check the equation as it is written.

Set up the model
The principal square root is nonnegative.
Substitute each candidate into the original equation.

Work the example
At x equals two, the square root of four equals two.
So two is a solution.
At x equals negative one, the square root of one is one, not negative one.
Negative one is not a solution.

Check the result
Now test negative two and three in the square root of x plus six equals x.
Take eight seconds to think before the answer appears.
[Eight-second silent pause to work; the answer remains hidden.]
Negative two fails because the square root of four is positive two.
Three works because the square root of nine is three.

Interpret the result
A candidate produced by squaring still needs an original-equation check.
Use the original task and check that your result fits its meaning.