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Question 664233: Megan factored the expression 18x^2+17x-15 as (2x-3)(9x+5). But when Jacob applied the FOIL principle and multiplied out (2x-3)(9x+5), he got 18x^2-17x-15; thus, Megan’s solution does not appear to check. Why is that? Please help Megan to understand this better. Explain your reasoning and correctly factor the original expression, if possible. If the expression is prime, so state. I am horrible at word problems and dont even know where to start. Can you Please help me out?!
Answer by ReadingBoosters(3246)   (Show Source):
You can put this solution on YOUR website! Lets check the FOIL on
(2x-3)(9x+5)
2x(9x) + 2x(5) - 3(9x) - 3(5)
Combine like terms
18x^2 + 10x - 27x - 15
18x^2 - 17x - 15 - Jacob was correct.
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18x^2 + 17x - 15
Megan was correct that there needs to be mixed signs due to positive 17 and negative 15; however, she made the resulting negative x coefficient larger producing a net negative sign instead of the original positive x coefficient.
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Megan only needs to reverse her signs to (2x+3)(9x-5) to factor correctly.
Check with FOIL
18x^2 - 10x + 27x -15, which combines to 18^2 + 17x - 15
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Delighted to help.
-Reading Boosters
Wanting for others what we want for ourselves.
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