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April 19, 2014

Posted by **Hannah** on Sunday, August 29, 2010 at 12:01am.

1) (x+8)^2 = x^2 + 64

2) (x-2)^3 = x^3 - 8

3) (x-2y)(x+y) = x^2 - xy -2y^2

4) (x+2)(x^2+3x-2) = x^3 + 5x^2 + 4x-4

Are my answers correct?

- Math(please check) -
**MathMate**, Sunday, August 29, 2010 at 8:59amNumbers 3) and 4) are correct.

For numbers 1) and 2), you have missed out terms, probably you have not used the right standard formulae.

(a+b)² = a² + 2ab + b²

(a-b)² = a² - 2ab + b²

(a+b)³ = a³ + 3a²b + 3ab² + b³

(a-b)³ = a³ - 3a²b + 3ab² - b³

If you are in an examination where you do not have an easy way to double check the standard formulae, you can treat

(a+b)² = (a+b)(a+b)

which you seem to have no problem solving.

- Math(please check) -
**Hannah**, Sunday, August 29, 2010 at 6:11pmso for (x+8)^2 i would use

a^2 + 2ab + b^2 and a would be 8 but what is b? Would it be 64?

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