solve by completeing the square

ginny1029

Junior Member
Joined
Apr 25, 2009
Messages
53
the instructions are solve by completing the square

the problem reads

2x^2 + 6x -56 = 0

i divide everything by 2 to get the x by itself and move the -56

2x^/2 + 6x/2_______ = 56/2

i now have
x^2 + 3x _______ = 28

i divide the 3 by 1/2 and get 3/2 and square it and get 9/4

x^2 + 3x + 9/4 = 28 + 9/4

i change the 28 to fourths and get

x^2 + 3x + 9/4 = 112/4 + 9/4

x^2 + 3x + 9/4 = 121/4

this becomes

(x + 3/2)^2 = 121/4

does this look right so far?
 
ok so i have (x + 3/2) ^2 = 121/4

now i go

x + 3/2 = plus or minus the square root of 121/4

x = -3/2 plus or minus the square root of 121/4

put im not sure were to go from there exactly do i need to simplify more?
 
What is the square root of 121? :wink:

Then combine the fractions....
 
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