SOLUTION: I need your help with, Factoring Trinomials By Grouping, If the Trinomials cannot be factored write "PRIME" 7b^2-42b+56

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Question 19884: I need your help with, Factoring Trinomials By Grouping, If the Trinomials cannot be factored write "PRIME"
7b^2-42b+56
Answer by vidyamanohar(13) About Me  (Show Source):
You can put this solution on YOUR website!
To factorize 7b^2-42b+56
the coefficients we see are 7, -42 and 56
7 is common factor of all these numbers
we write 7b^2-42b+56=7(b^2-6b+8)
8 can be written as the product of 4 and 2 but their sum is 6 but not -6. So we try -4 and -2 which suits the requirement
7(b^2-6b+8)=7(b^2-4b-2b+8)=7(b-4)(b-2)