Foil Method to simplify (9c+d)(9c-d)

[jburgswife30]

(9c+d)(9c-d)

81c^2-9cd+9cd-d^2
81c^2-cd-d^2

Is this done the right way

 

[arthur ohlsten]

Re: Foil Method

you did it the right way but 9cd-9cd=0 that was your error


[9c+d][9c-d]
First=9c*9c
Outer=9c*[-d]
Inner=d*9c
last=d*[-d]

[9c+d][9c-d]=81c^2-9cd+9cd-d^2
=81c^2-d^2
Arthur

 

[jburgswife30]

Re: Foil Method

thank you, I thought there was a mistake.

 

[tkhunny]

Re: Foil Method

(9c+d)(9c-d)

81c^2-9cd+9cd-d^2
81c^2-cd-d^2

Is this done the right way

If you relied on FOIL, rather than simply learning to multiply, I'd have to say that it was not done the "right way". The more you rely on FOIL, the more you will be confused where a factor has three terms.

 

[stapel]

Re: Foil Method

The more you rely on FOIL, the more you will be confused where a factor has three terms.

...and the more you will be confused when a factor is not a binomial! :shock:

Eliz.