## EmmaH 2 years ago Multiply: (3a + 11)(3a - 11). 9a2 - 22 9a2 - 121 9a2 + 121 9a2 - 66a + 121 i know its either b or c but i donmt knwo which it is..

1. JayDS

Do you know the crab claw/Foil method to expand out the brackets?

2. ZeHanz

This is the form: (a-b)(a+b) = a²-b². It pays to learn this form by heart, so you can recognise them immediately when you see one!

3. precal

this is a difference of squares as ZeHanz stated

4. JayDS

yes it is indeed but she can easily get the answer if she expands the brackets and collect like terms as well.

5. EmmaH

ii got the answer usinmg foil which is 9a^2+ (-121)

6. ZeHanz

FOILing is fine! It's just that in SOME cases, you don't need it, because you can see the answer right away. This is such a special case. Another one: (3p+4q)(3p-4q). See: sum and difference of the same two numbers, so the answer is (3p)²-(4q)²=9p²-16q². You can save so much (spare) time with this...

7. EmmaH

but my answermy answer possiblities are 9a2 - 22 9a2 - 121 9a2 + 121 9a2 - 66a + 121

8. JayDS

The answer you got from FOILING is correct, 9a^2+ (-121). but one thing, you forgot that + - becomes - 9a^2 -121

9. JayDS

Also note for special cases as these u should learn them, so u are able to identify them straight away just as @ZeHanz shows it.

10. EmmaH

thank you peoples!

11. ZeHanz

Welcome!

12. precal

never use double signs|dw:1359206802362:dw|