Answer: (m-21)(m+1)
Step-by-step explanation:
To factor this trinomial, find two numbers that multiply to -21 and add to -20:
(-21)(1)=-21
-21+1=-20
They are -21 and 1.
Add -21 and 1 to m to get both factors:
(m+(-21)) and (m+1)
(m-21) and (m+1)
Multiply them to get the answer:
(m-21)(m+1)