Question

Solve this equation: (x + 4) (x - 4) = 9

Answer 1

`x=5` or
`x=-5`

Explanation:

`(x+4)(x-4)=9`

Simplify.

`x2-16=9`

Add 16 to both sides.

`x2-16+16=9+16`

`x^(2) =25`

Take the square root.

`x = √(25)`

`x = 5` or
`x = -5`

Answer 2

x = 5, x = -5 are your answers

Explanation:

First, FOIL (First, Outside, Inside, Last)

(x + 4)(x - 4) = 9

x(x) = x²

x(-4) = -4x

4(x) = 4x

4(-4) = -16

x² - 4x + 4x - 16 = 9

Simplify. Combine like terms

x² (-4x + 4x) - 16 = 9

x² - 16 = 9

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Isolate the x. Note the equal sign. What you do to one side, you do to the other. Do the opposite of PEMDAS.

First, add 16 to both sides

x² - 16 (+16) = 9 (+16)

x² = 25

Next, isolate the x completely by rooting both sides

√(x²) = √(25)

x = √25

x = √25 = √(5 x 5)

x = √25 = √(-5 x -5)

x = 5 , -5

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x = 5, x = -5 are your answers

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