Answer
$48xy$
Work Step by Step
The square of a binomial sum is: $(A+B)^2=A^2+2AB+B^2$.
The square of a binomial difference is: $(A-B)^2=A^2-2AB+B^2$.
Hence here: $(3x+4y)^2-(3x-4y)^2=(3x^2)+2\cdot3x\cdot4y+(4y)^2-[(3x^2)-2\cdot3x\cdot4y+(4y)^2]=24xy-(-24xy)=48xy$
