Posted by **Marina** on Monday, October 3, 2011 at 7:38am.

1.) 4(2-a)^2-81

2.) -(x-y)^3

3.)3x^2-27(2-x)^2

4.) 9(y-1)^2-25

- Math help please -
**Reiny**, Monday, October 3, 2011 at 9:04am
1. 4(2-a)^2 - 81 , difference of squares

= (2(2-a) + 9)(2(2-a) - 9)

=(4 - 2a +9)(4 -2a - 9)

= (-2a + 13)(-2a - 5)

or

(2a-13)(2a+5) , I wanted to start the brackets with a positive so I multiplies by (-1)(-1)

Do #4 the same way.

3.

3x^2 - 27(2-x)^2

= 3[x^2 - 9(2-x)} , again a difference of square

= 3(x - 3(2-x))(x + 3(2-x))

= 3(x - 6 + 3x)(x + 6 - 3x)

= 3(4x-6)(6-2x)

= 3(2)(2)(2x-3)(3-x)

= 12(2x-3)(3-x)

For #2,

-(x-)(x-y)(x-y)

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

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

= - x^3 + 3yx^2 -3xy^2 + y^3

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