foil
first
outer
inner
last
example if you had
(x+y)(z+t)
first x times z
outer x time t
inner y times z
last y times t
so
FOIL
(t+2bs^2)(2t-3bs^2)
FIRST (t times 2t=2t^2)
Outer (t times -3bs^2=-3tbs^2)
Inner (2bs^2 times 2t=4tbs^2)
Last (2bs^2 times -3bs^2=-6b^2s^4)
now add
2t^2-3tbs^2+4tbs^2-6b^2s^4
add like terms (-3tbs^2+4tbs^2=1tbs^2=tbs^2)
2t^2+tbs^2-6b^2s^4
