(2x + 3y)^2 – (2x – 3y)^2 = 360 show that xy is a multiple of 5

  • Google+ icon
  • LinkedIn icon
  • 1124 views

Expand first brackets:

4x2+6xy+6xy+9y2

Expand second brackets:

4xy2-6xy-6xy+9y2

Subtract the second expansion from the first one, being careful of the double negative:

=24xy

Then, back into the original equation:

24xy=360

Divide both sides by 24:

xy=15

Divide by 5:

(xy)/5=3

The result is an integer, so xy is a multiple of 5

Ryan M. GCSE Biology tutor, A Level Biology tutor, GCSE Chemistry tut...

About the author

is an online GCSE Maths tutor with MyTutor studying at Birmingham University

Still stuck? Get one-to-one help from a personally interviewed subject specialist.

95% of our customers rate us

Browse tutors

We use cookies to improve your site experience. By continuing to use this website, we'll assume that you're OK with this. Dismiss

mtw:mercury1:status:ok