Answer
$9x^2-42x+49$
Work Step by Step
A binomial squared is equal to the square of the first term plus or minus twice the product of both terms plus the square of the second term.
$(a - b)^2= a^2 - 2ab + b^2$
$(3x-7)^2=(3x)^2-2(3x)(7)+7^2=9x^2-42x+49$
