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How do I solve this by completing the square?

How do I solve this by completing the square?-example-1
User Avi Levin
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x^2 + 2x - 5 = 0

Keep the x^2-term and the x-term on the left side. Add 5 to both sides to get rid of the -5 from the left side.

x^2 + 2x = 5

The term you need to add to the left side to complete the square is the square of half of the coefficient of the x-term. The x-term is 2x. The coefficient of the x-term is 2. Half of 2 is 1. 1 squared is 1. That means you need to add 1 to the left side to complete the square. The rule with equations is that you need to add the same thing to both sides of the equation, so we must add 1 to both sides.

x^2 + 2x + 1 = 5 + 1

x^2 + 2x + 1 = 6

Now the left side is a perfect square. You can express it as the square of a binomial.

(x + 1)^2 = 6

There is a rule: if w^2 = k, k being a non-negative number, then w = sqrt(k) or w = -sqrt(k). We now apply his rule. In our case, our w is x + 1.


x + 1 = √(6) ~~or~~x + 1 = -√(6)

Now we solve each equation above by subtracting 1 from both sides.


x = -1 + √(6) ~~ or~~ x = -1 - √(6)

User Ketysek
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User Bachalo
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