use FOIL method
first
outer
inner
last
ex.
(3x+2y)(5x+7y)
multiply the first terms
(3x)(5x)=15x(squared)
multiply the outer terms
(3x)(7y)=21xy
multiply the inner terms
(2y)(5x)=10xy
mulitply the last terms
(2y)(7y)=14y(squared)
and add the product of the outer and inner terms
21xy + 10xy=31xy
answer:
15x(squared) + 31xy + 14y(squared)
