Multiplying out quadratics

Last Friday, we looked at multiplying out quadratic expressions like

(x + 2)(x + 3) = x² + 3x + 2x + 6 = x² + 5x + 6.

As the BBC Bitesize page explains, you multiply everything in the first bracket by the things in the second bracket, so you obtain four terms. Two of the terms are x terms, and so these can be added together. One way of remembering to multiply out the terms so you capture them all is FOIL

• First - the first term in each bracket, x multiplied by x gives x²
• Outer - the first thing in the first multiplied by the last in the second bracket, x times 3 in this case
• Inner - the 2 times x in this case
• Last - the 2 times the 3 in this case

As always you need to watch the signs!

Try this Web quiz - check your multiplying out of quadratics. A new window will appear with a question and four possible answers, choose the answer you think is right, you should get some feedback. If no questions appear, you need to check that JavaScript is ‘permitted’ by your Web browser.

Close the window after trying the quiz. When you re-load the quiz, you will get a different random choice of 10 questions from 20 questions. I wrote the quiz myself using Hot Potatoes, a free quiz generator program written by a Canadian English teacher.

This entry was posted on Sunday, March 11th, 2007 at 1:37pm and is filed under Algebra. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response or trackback from your own site.