Question

(7x+8y)^2

Answer 1

\[(ax + by)^2 = a^2x^2 + b^2y^2 + 2(ax)(by)\]

Answer 2

(7x + 8y)^2 =

(7x + 8y)(7x + 8y)
we will use the FOIL method (first, outside, inside, last)

First -- multiply the 1st numbers in each set... 7x * 7x = 49x^2
Outside -- multiply outside numbers in each set...7x * 8y = 56xy
Inside -- multiply inside numbers in each set...8y * 7x = 56xy
Last -- multiply last numbers in each set...8y * 8y = 64y^2

now put it all together..
49x^2 + 56xy + 56xy + 64y^2 -- combine like terms
49x^2 + 112xy + 64y^2 <== your answer