Examples

Solve by Completing the Square
x2-8x-1=0
Step 1
Add 1 to both sides of the equation.
x2-8x=1
Step 2
To create a trinomial square on the left side of the equation, find a value that is equal to the square of half of b.
(b2)2=(-4)2
Step 3
Add the term to each side of the equation.
x2-8x+(-4)2=1+(-4)2
Step 4
Simplify the equation.
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Step 4.1
Simplify the left side.
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Step 4.1.1
Raise -4 to the power of 2.
x2-8x+16=1+(-4)2
x2-8x+16=1+(-4)2
Step 4.2
Simplify the right side.
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Step 4.2.1
Simplify 1+(-4)2.
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Step 4.2.1.1
Raise -4 to the power of 2.
x2-8x+16=1+16
Step 4.2.1.2
Add 1 and 16.
x2-8x+16=17
x2-8x+16=17
x2-8x+16=17
x2-8x+16=17
Step 5
Factor the perfect trinomial square into (x-4)2.
(x-4)2=17
Step 6
Solve the equation for x.
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Step 6.1
Take the specified root of both sides of the equation to eliminate the exponent on the left side.
x-4=±17
Step 6.2
Add 4 to both sides of the equation.
x=±17+4
x=±17+4
Step 7
The result can be shown in multiple forms.
Exact Form:
x=±17+4
Decimal Form:
x=8.12310562,-0.12310562
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