Question

If the 3rd term and the 9th term of an AP are 4 and -8 then which term of these AP is 0.

Answer 1

Step-by-step explanation:

a+2d = -1

a+6d = 11

subtract them:

4d = 12

d = 3

from a+2d = -1 , a = -7

term(n) = a+(n-1)d

= -7 + 3(n-1)

= -7 + 3n - 3

= 3n - 10

"the numbers of which must be added to get a sum of 430"

I will assume you mean, "how many terms are needed to have sum of 430" ?

sum(n) = (n/2)(first + last)

430 = (n/2)(-7 + 3n-10)

860 = n(3n - 17)

3n^2 - 17n - 860 = 0

(n - 20)(3n + 43) = 0  

n = 20 or n = -43/3, the latter would be extraneous

you will need 20 terms

Answer 2

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