Answer
$(7g-6)^{2}$
Work Step by Step
$49g^{2}-84g+36=$
...write first and last terms as squares.
$=(7g)^{2}-84g+6^{2}$
...does middle term equal $2ab$?
$84g=2\cdot(7g)\cdot(6)$
$=(7g)^{2}-2\cdot(7g)\cdot(6)+6^{2}$
...write as the square of a binomial.
$=(7g-6)^{2}$
