Respuesta :

FOIL
first
outer
inner
last
example if you had
(a+b)(c+d)
first a times c
outer a times d
inner b times c
last b times d

(2x-7)(x+3)
first 2x times x=2x^2
outer 2x times 3=6x
inner -7 times x=-7x
last -3 times 3=-21

add them
2x^2+6x-7x-21
2x^2-x-21
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