How do i expand this factored equation? y=8(x+6)(x-9)?

Question

I forget what to do with the 8 outside two sets of brackets. I remember without a number outside or variable you use the foil method, but I'm not sure what to do with an 8 outside the brackets.

Thanks in Advance!

? · Accepted Answer

First way is done by expanding the brackets first, leaving the 8 there. It might help to visualise with an extra pair of brackets. Once you’ve expanded and got your result, multiply by 8 (expand again). 
Another way is by multiplying what’s in the first bracket by 8. Keep the brackets. Then expand again.

? · Answer

y = 8(x^2 - 3x -54) = 8x^2 - 24x - 432.

llaffer · Answer

y = 8(x + 6)(x - 9)

Recall that you can multiply numbers in any order and end up with the same product.

I would ignore the 8 first and then foil the two binomials, first:

y = 8(x² - 3x - 54)

Now multiply the 8 into each term of the trinomial:

y = 8x² - 24x - 432

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If you wanted to multiply the 8 by the first binomial first you could, then multiply the remaining binomials.  We should get the same result:

y = 8(x + 6)(x - 9)
y = (8x + 48)(x - 9)
y = 8x² - 72x + 48x - 432
y = 8x² - 24x - 432

Either way, we get the same result.

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How do i expand this factored equation? y=8(x+6)(x-9)?

3 Answers