## Inopeki 3 years ago FOILing, do i multiply or add? Like (2x+4)+(2x+4) i add there, right? And (2x+4)*(2x+4) I multiply there, right?

1. satellite73

yes

2. Inopeki

I did that in class todya but i didnt get the right answer..

3. satellite73

what did you get for the first one?

4. Inopeki

(2x+4)+(2x+4) 4x+2x+4+4+2x+4+4 8x+16

5. satellite73

hmm

6. satellite73

7. amistre64

when it says to add, I would add. and when it says to multiply, id multiply. but thats just me set in my ways :)

8. satellite73

$(2x+4)+(2x+4)=2x+4+2x+4=2x+2x+4+4$

9. satellite73

let's imagine for a moment that x was ten (x is a variable, but it could be ten) then $2x+4=2\times 10+4=24$ and $24+24=48$

10. Inopeki

I thought it was like this |dw:1327066387934:dw|

11. satellite73

multiplication distributes over addition. so if you had $(2x+4)(2x+4)$ you would use the distributive law, just like if you had $24\times 24$

12. Inopeki

But wheres the x?

13. Tomas.A

addition is commutative you can remove brackets when you have ONLY addition

14. satellite73

but addition is the same as "combine like terms" just as you would with arithmetic 24 + 24 ______ 48 2x + 4 + 2x + 4 __________ 4x + 8

15. amistre64

2x+4 (+) 2x+4 -------- 4x+ 8 2x+4 (x) 2x+4 --------- 8x+16 4xx+8x ----------------- 4x^2+16x+16

16. Inopeki

Why would it be 4x^2+16x+16?

17. satellite73

@inopeki i was making an analogy. the work you do with variables is a generalization of the work you do in arithmetic, and if it doesn't work with arithmetic it certainly doesn't work with variables, because the variable could be a number, that is you could replace the variable by a number

18. amistre64

becasue thats what happens when you multiply stuff

19. Inopeki

Oh ok

20. Inopeki

so basically just add them up?

21. Inopeki

2x+4 (+) 2x+4 -------- 4x+ 8

22. satellite73

imagine your job was to add $24+24$\ what would you do? line them up and add

23. amistre64

5+3 = 8 (x) 2+4 = 6 ------------ 20+12 10+6 -------------- 10+26+12 = 48

24. Inopeki

24 +24 ---- 48

25. satellite73

and similarly 2x + 4 + 2x + 4 __________ 4x + 8

26. Inopeki

Oh! Give me another example?

27. satellite73

$(3x+5)+(4x+1)$

28. Inopeki

(3x+5) +(4x+1) -------- 7x+6

29. satellite73

that's it!

30. Inopeki

Yes! :D Thanks