Find the term indicated in the expansion.

(x - 3y)11; 8th term

A. -721,710x7y4
B. -721,710x4y7
C. 240,570x7y4
D. 240,570x4y8

Question

Find the term indicated in the expansion.

(x - 3y)11; 8th term

	A. -721,710x7y4 	
	B. -721,710x4y7 	
	C. 240,570x7y4 	
	D. 240,570x4y8

anonymous · Answer

I believe it's one of either A or B?

campbell_st · Answer

well its binomial expansion 

$$(a + b)^n  $$

where a term can be found using 

$$^nC_{r}(a)^{n - r}(b)^r$$

so in your question you need the 8th term... so r = 7..... since the 1st term r = 0

so you are looking at 

$$^{11}C_{7} (x)^{11 - 7}(-3y)^7$$

you just need to simplify it

anonymous · Answer

Frankly, you lost me a little bit.

campbell_st · Answer

so do you know about binomial theory... and how the coefficients can be found using combinations...?

anonymous · Answer

I know the theory, the combinations not so much. Is that C? Because that was what confused me.

campbell_st · Answer

yes... some texts use bracket notation 
|dw:1367012076196:dw|