Write it like this:
(7x+3y)(7x+3y)
Our teacher tells us to Foil, which means we multiply the Firsts, the OUters, the Inners, and the Lasts. If you do this, you get
7x(7x) + 7x(3y) + 7x(3y) + 3y(3y)
49x^2 + 21xy + 21xy + 9y^2
49x^2 + 42xy + 9y^2
(7x+3y)^2
3 answers
(a+b)^2=a^2+2*a*b+b^2
(7x+3y)^2=(7x)^2+2*7x*3y+(3y)^2=4+9x^2+42xy+9y^2
(7x+3y)^2=(7x)^2+2*7x*3y+(3y)^2=4+9x^2+42xy+9y^2
Correction:
(7x+3y)^2=(7x)^2+2*7x*3y+(3y)^2=49x^2+42xy+9y^2
(7x+3y)^2=(7x)^2+2*7x*3y+(3y)^2=49x^2+42xy+9y^2