Answer
$(x-7)^2$
Work Step by Step
The first term in each binomial must be x, since $x^2$ has no coefficient.
The operation in each binomial must be subtraction, since the trinomial has a positive and a negative term.
$-7+(-7)=-14$ and $-7\times(-7)=49$, so the other two terms are -7 and -7.
Since the two binomials contain the same expression they are written with an exponent of 2,
