Question

Multiply (3A+4B)(3A-4B)? ?

Answer 1

I don't get this at all....

Answer 2

9a^2-16b^2

Answer 3

See I got the 9A^2 but I couldn't get the second part.

Answer 4

you use the FOIL rules. which would be 3a x 3a, then you do 3a times -4b, and 3a times bb. the two 3a x 4b cancle eachother because one is - and one is +. the final part is 4b x -4b which equals 16b^2

Answer 5

that make more sense?

Answer 6

\[3A \times 3A + 3A \times -4B +4B \times 3A + 4B \times -4B\]
\[=9A ^{2} -12AB +12AB -B ^{2}\]
\[=9A ^{2}-4B ^{2}\]

Answer 7

Yes I think so. I don't really remember learning FOIL. Thank you

Answer 8

use this method (If you can imagine it in table form with 3A+4B in the column headings, and in the row headings 3A and -4B) sorry can't show the lines.

3A 4B

3A 9A^2 +12AB

-4B -12AB -16B^2

now add the boxes 9A^2 +12AB
-12AB -16B^2
=9A^2 -16B^2

Answer 9

it stands for First, Outside, Inside, Last. the order that i multiply the four parts of that sort of problem

Answer 10

After a while, you get to learn (for this type of question), the rule of the difference of 2 squares.
(x+y)(x-y) = x^2 -y^2
here x = 3A
y= 4B
so you can go immediately to
(3A+4B)(3A-4B) = (3A)^2 - (4B)^2
= 9A^2 - 16B^2
Same as before

Answer 11

I learnt the smiley face method instead of foil both are just as valid

Just make sure you end up with four parts before cancelling