How do you solve using the completing the square method #x^2 – 8x + 13 = 0#?

1 Answer
Jun 28, 2016

Answer:

#x = 5.732 or x = 2.268#

Explanation:

The method of completing the square is based on the fact that there is a pattern in the answer of squaring a binomial.

#(x - 5)^2 = x^2 - 10x +25 " Note "(10/2)^2 = +25#

The square of (half of the coefficient of x), gives the last term.

So let's find the missing term ....

#x^2 - 14x + ......color(red)(??).... rArr x^2 - 14x + color(red)(7^2)#

#x^2 + 22x + .....color(blue)(??).. rArr x^2 + 22x + color(blue)(11^2)#

Once you have all three terms, you can write them as #(x +- ...)^2#

#x^2 - 14x + color(red)49 = (x -color(red)7)^2 " -14÷2 = -7, or "sqrt49 =7#

#x^2 + 22x + color(blue)121 = (x + color(blue)11)^2#

Now for your question....

#x^2 -8x +13 =0 " move 13 to the right side"#

#x^2 -8x + 16 =-13 +16 " add 16 to both sides"#

#(x-4)^2 =3 " Write as a square"#

#x - 4 = +-sqrt3" square root both sides"#

#x = sqrt3 +4 or x = -sqrt3+4" solve for x twice"#

#x = 5.732 or x = 2.268#