Solve this eqution: (x+3)(x+9)

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kjcdb8er's profile pic

kjcdb8er | Teacher | (Level 1) Associate Educator

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As written, the expression (x + 3)(x + 9) is not an equation, so there is nothing to solve. This expression may be simplified by multiplying through the parenthesis.

(x + 3)(x + 9) = (x + 3)*x + (x + 3)*9

= x^2 + 3x + 9x + 3*9

= x^2 + 12x + 27


Often expressions such as that given are set equal to zero, in which case there is an equation.

(x + 3)(x + 9) = 0 may be solved by remembering that if a*b = 0, then either a or b must be equal to zero. Thus either x + 3 = 0 or x + 9 = 0, meaning that x = -3 or x = -9

taangerine's profile pic

taangerine | Student, Grade 12 | (Level 1) Valedictorian

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To solve this equation, we can use FOIL -- First, Outside, Inside, Last

  • (x)(x)+(9)(x)+(3)(x)+(9)(3)


  • `x^(2)+9x+3x+27`
  • `x^(2)+12x+27`
crystaltu001's profile pic

crystaltu001 | Student, Grade 10 | (Level 1) Valedictorian

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Use the foil method and distribute the first  x and the 3 to the other numbers.

x*x= x^2

x*9= 9x

3*x= 3x


The answer is x^2+12x+27

acompanioninthetardis's profile pic

acompanioninthetardis | Student, Undergraduate | (Level 1) Valedictorian

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(x+3)×(x+9). You have to take one part I.e. X and then multiply it to the entire second equation I.e. x+9. And then put the same sign as in the middle in this case it's addition and then repeat the first step but multiply by 3 so you get something like this X squared + 9x +  3x + 27. Then simplify to x^2 +12x+27.

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zumba96 | Student, Grade 11 | (Level 3) Valedictorian

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For (x+3)(x+9) you have to use FOIL

Take; x(x+9)+3(x+9) 

= x^2+9x+3x+27

Combine Like Terms


Wiggin42's profile pic

Wiggin42 | Student, Undergraduate | (Level 2) Valedictorian

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I am assuming the problem is this: 

(x+3)(x+9) = 0 

We know that either

x + 3 = 0    or    x + 9 = 0

Solve for the two different x values independently and get: 

x = -3      x = -9

Depending on the real life application (if there is one for this problem) one of the answers is extraneous. 

atyourservice's profile pic

atyourservice | Student, Grade 11 | (Level 3) Valedictorian

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use the foil method, multiply every number in the first parentheses by every number in the second parentheses:

`(x+3)(x+9) `

`x xx x=x^2 `

`x xx 9=9x `



`x^2+9x+3x+27 `

combine like terms which would be `9x+3x=12x`


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Jyotsana | Student, Grade 10 | (Level 1) Valedictorian

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Box Method








mh41602's profile pic

mh41602 | Elementary School Teacher | (Level 1) eNoter

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These questions are made into equations so you can solve them. The key is to make both sides of the equation equal. I call it balancing the scale.

Start with (x+3)(x+9)=0

Then FOIL Method


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