Get out the calculator. 12.5, X, =. Calculator says 156.25. Not 25.
You want the number when multiplied by itself is equal to . BUT don't stop there. Once you recall from your 3rd grade multiplication tables which number times itself equals 25 you only have half the answer. That is because a positive number times a positive number is a positive number, but a negative number times a negative number is ALSO a positive number. That means both the positive and the negative of the value are answers to this problem.
The fact that this problem has two answers makes good sense -- the Fundamental Theorem of Algebra says that a non-zero polynomial equation with complex coefficients has as many roots, counting multiplicities, as the degree of the polynomial. You have a polynomial of degree 2, so there has to be two roots.
