Question

how many terms of AP 4,7,10______should be taken so that sum is 1000​

Answer 1

Answer:

n=25

Step-by-step explanation:

a= 4

d= 7-4=3

Sn=1000

n=?

Sn=n/2[2a+(n-1)d]

1000 = n/2[2×4+(n-1)3]

1000 = n/2[8+3n-3]

1000 = n/2 (5+3n)

1000 × 2 = n(5+3n)

2000 = 5n + 3n2

3n2 + 5n -2000 =0

3n2 +80n-75n -2000 = 0

n(3n+80) -25(3n +80) = 0

(3n+80)(n-25) =0

3n+80=0. n-25=0

n=-80/3. n=25

As , terms can't be in fraction or negative.

Therefore, no. of terms us equal to 25.

n=25

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