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