How do you solve #x^2 - 30 = 8x# by completing the square?

Question

2455 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2015-05-12T21:14:50

First subtract #8x# from both sides to get #x^2 - 8x - 30 = 0#.

#(x-4)^2 = x^2 - 8x + 16#

So:

#0 = x^2 - 8x - 30#

#= x^2 - 8x + 16 - 16 - 30#

#= (x-4)^2 - 46#

Add 46 to both sides to get

#(x-4)^2 = 46#

So we have

#x - 4 = +-sqrt(46)#

Add 4 to both sides to get

#x = 4 +-sqrt(46)#