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​Algebra 1   State Test Practice

How to solve by completing the square

1/24/2019

 
Solve the equation  x² + 6x = -11/4
A.)  x = -3 and 2
B.)  x = -2 and 3
C.)  x = 1/2 and -11/2
​D.)  x = -1/2 and -11/2

Nobody ever likes completing the square, so we'll go with that method!

x² + 6x = -11/4
x² + 6x + 9 = (-11/4) + 9   {took half of coefficient of x, squared it, and added to each side....that completes the square}
(x + 3)² = 25/4   {factored the left side and added -11/4 and 9}
x + 3 = ±5/2   {took square root of each side}
x = -3 ± (5/2)   {subtracted 3 from each side}
x = (-6/2) ± (5/2)   {got common denominator}
x = -1/2   or  -11/2   {added and subtracted, using the ± sign}

D.)  x = -1/2  and  -11/2

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