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## lawls 2 years ago Find the 7th term of (x^2 + 3y)^9

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1. amistre64

looks like a pascal

2. amistre64

given: \[(p+q)^n\] we can work out the middle stuff as:\[p^{n-c}q^c\] the coeeficient is a little tricker unless you know about combinatorics

3. amistre64

and c is the "term" value :)

4. amistre64

n choose c is what i think i recall for the coeff; or else draw up the pascal triangle

5. shubhamsrg

|dw:1358788894374:dw| This is the working formula.

6. amistre64

that looks about right, but if i remember it correctly: the first term starts at 9 and drops down till it hits the 7th term

7. shubhamsrg

Didn't get you ?

8. shubhamsrg

The first term's coefficient is 1 , when r=0,

9. amistre64

(a+b)^9 a^9 a^8 a^7 a^6 a^5 a^4 a^3 ^^^ b^0 b^1 b^2 .... b^6 ^^^ these always get turned around in my head

10. lawls

ok thanks

11. amistre64

good luck ;)

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