Question

Find the missing term in the following expression to make each a perfect square.
$4x^2-\square +49$

Answer 1

${4x}^2-+49$

${\left(2x\right)}^2-\underset{–}{2\times 2x\times 7}+{(-7)}^2$

${\left(2x\right)}^2-28x+49$

${(2x-7)}^2$

Using the identity

${(a-b)}^2=a^2-2ab+b^2$

Hence the missing term is $28x$.