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Are the following results correct:1. (x+5)(x+2) = x^2 + 7x + 10x. 2. (x-2)(x-2) = x^2 +...

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anya4one | Student, Undergraduate | (Level 2) Honors

Posted August 4, 2011 at 2:39 AM via web

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Are the following results correct:

1. (x+5)(x+2) = x^2 + 7x + 10x.

2. (x-2)(x-2) = x^2 + 4x +4x

3. (x-5)(x+12) = x^2 + 7x - 60

4. (3c-5d)(2c+4d) = 6c^2 + 2cd^2 +20d^2

5. 5x-3)(3x-8) = 15x - 49x + 24

2 Answers | Add Yours

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justaguide | College Teacher | (Level 2) Distinguished Educator

Posted August 4, 2011 at 3:01 AM (Answer #1)

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The result of (x + a)(x + b) = x^2 + (a + b)*x + ab

The correct results for your problems are:

1. (x+5)(x+2) = x^2 + (5 + 2)x + (5*2) = x^2 + 7x + 10

2. (x-2)(x-2) = x^2 + (-2 - 2)x + (-2)*(-2) = x^2 - 4x + 4

3. (x-5)(x+12) = x^2 + (-5 + 12)x + (-5*12) = x^2 + 7x - 60

4. (3c-5d)(2c+4d) = 6c^2 + 12 cd - 10cd - 20d^2 = 6c^2 + 2cd - 20d^2

5. (5x-3)(3x-8) = 15x^2 - 40x - 9x + 24 = 15x^2 - 49x + 24

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aimeefarnum | High School Teacher | (Level 2) Adjunct Educator

Posted August 4, 2011 at 4:08 AM (Answer #2)

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Use FOIL to complete these problems.

First (First item in each bracket multiplied together)

(x+5)(x+2)

Outer (outside two items )

(x+5)(x+2)

Inner (inside two items)

(x+5)(x+2)

Last (last two items)

(x+5)(x+2)

Your mistake on these was adding an x and the end of the last set on the first two problems.  The Last two numbers to multiply for number 1 are

(x+5)(x+2) 5 and 2.  5x2 is 10, not 10x.

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