Answer: 4(4b - 5)(b + 5)
Step-by-step explanation:
All have a common factor of 4
4(4b^2 + 15b - 25)
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Now you need to find two numbers that:
a) multiply to -100 (the a term * the c term = 4 * -25)
b) add to 15 (the b term)
After a little thinking, we can determine that the two numbers are:
20 and -5
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Now we can rewrite the middle term as 20b - 5b (notice how it still equals 15b)
4(4b^2 + 20b - 5b - 25)
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4((4b^2 + 20b) + (-5b - 25))
Group the terms (associative property)
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Take out a common factor from each
4(4b(b + 5) - 5 (b + 5))
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Now we can factor by grouping
4(4b - 5)(b + 5)
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