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san4es73 [151]
3 years ago
15

3x squared -42x+9=-5 for completing the square

Mathematics
1 answer:
enot [183]3 years ago
8 0
3x^2 -42x + 9 = -5

Subtract 9 from both sides
3x^2 -42x  = -5 - 9

3x^2 -42x  = -14

Divide by 3 through
x^2 -14x  = - \dfrac{14}{3}

Add (b/2)^2 to form perfect square
x^2 -14x +  (\dfrac{14}{2})^2  = - \dfrac{14}{3} +  (\dfrac{14}{2})^2

Form perfect square
(x -7)^2  =  \dfrac{7}{3}

square root both sides
(x -7) = \pm \sqrt{\dfrac{7}{3}}

Add 7 to both sides
x  =   \pm \sqrt{\dfrac{7}{3}}  + 7

Rewrite the answer into 2 different answers
x  =   7 +  \sqrt{\dfrac{7}{3}}  \ or \  7 - \sqrt{\dfrac{7}{3}}



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