How do you factor the trinomial #3r^2+2r-21#?

1 Answer
Jan 6, 2016

#(3r -7)(x + 3)#

Explanation:

If a trinomial can be factored, the factors of #(ax + b)(cx + d)# will give #acx^2 + (ad +bc)x + bd#. We therefore need factors of #3# and #-21# that will combine to give #2#.
The only possible factors of #3# are #3# and #1#. The appropriate factors of #-21# are #-7# and #3#
#3r^2 +2r - 21 = (3r -7)(x + 3)#