Question

In an AP , sum of the first ten terms is -150 and the sum of its next ten terms is -550. Find the AP​

Answer 1

Answer:given s10 = -150

-150 = n/2 ( 2a + (n-1)d)

-150 = 5(2a + 9d)

2a + 9d = -30........(1)

S20 = -550

-550 = n/2(2a + (n-1)d

-550 = 10(2a + 19d)

2a + 9d = -55 .......(2)

FROM (I) AND (2) BY ELIMINATION

2a + 9d = -30

2a + 19d = -55

-     -           +

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     -10d = 25

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d = -2.5 put d = -2.5 in eq (1)

2a + 9 (-2.5) = -30

2a = -30+22.5

2a = -7.5

a = -3.75

AP is -3.75 , -6.25 , -8.75 , -11.25..............

hope this hlpful

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