Asked by Alisha Naqvi
In an A.P , the sum of first ten terms is (-80) and the sum of its next ten terms is (-280)Find the A.P
Answers
Answered by
oobleck
So plug in your formula. If S1 is the sum of the 1st ten terms, and S2 is the sum of the 1st twenty terms, then you have
S1 = 10/2 (2a+9d) = -80
S2 = 20/2 (2a+19d) - S1 = -280
Rearranged a bit, that's
10a + 45d = -80
10a + 145d = -280
Looks like
a = 1
d = -2
S1 = 10/2 (2a+9d) = -80
S2 = 20/2 (2a+19d) - S1 = -280
Rearranged a bit, that's
10a + 45d = -80
10a + 145d = -280
Looks like
a = 1
d = -2
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