The Student Room Group

Math inequalities help

Gosh, okay this seems like a simple question but:

Attachment not found


Why is the (2k) [outside the bracket] to the power of 2
Capturesds.PNG
(edited 6 years ago)
Post it please so we can help.
Original post by CorpusLuteum
Gosh, okay this seems like a simple question but:


Why is the (2k) outside the bracket to the power of 2


Attachment not found
I cannot see the attachment but you're asking why is 2k in bracket? Well, (x+2k)^2 when expanded will yield an extra (2k)^2 term which you don't, hence you subtract it.
Original post by RDKGames
Attachment not found


Okay I think it worked now?
Original post by CorpusLuteum
Gosh, okay this seems like a simple question but:

Attachment not found


Why is the (2k) outside the bracket to the power of 2
Capturesds.PNG


actually attach your attachment !!
Original post by CorpusLuteum
Okay I think it worked now?


yes, it worked, now.

do you know how to complete the square?

Can you complete the square and solve

x^2 - 4x -1 = 0 ??
x^2+4kx-k = 0 --> (x+2k)^2-(2k)^2-k=0.

E.g. x^2+6x+10 --> (x+3)^2 - 3^2 + 10 --> (x+3)^2 + 1. It's how completing the square works; you generate an extra term that should be subtracted.
Original post by CorpusLuteum
Okay I think it worked now?


Because (x+2k)2=x2+4kx+4k2(x+2k)^2 = x^2+4kx+4k^2 but you only want the first two terms, hence x2+4kx=(x+2k)24k2x^2+4kx = (x+2k)^2-4k^2, but 4k2=(2k)24k^2 = (2k)^2 hence that's where it comes from.

Quick Reply