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If the 11^( th ) term of an A.P.is - 21 and the sum of first 7 terms is -49 find the A.P

Posted by Good Student 5 years, 2 months ago

CBSE > Class 10 > Mathematics

2 answers

Sahil Kumar 5 years, 2 months ago

11th term=a+(11-1)d=(-21) a+10d=(-21) a=(-21-10d) Sum of first 7th term =7/2(2×a+(7-1)(d) =7(a+3d) =7(-21-10d+3d) =7(-21-7d) =49(-3-d) But,49(-3-d)=(-49) -3-d=(-1) d=(-2) a=-21-10(-2)=(-1) AP=(-1),(-3),(-5).......

1Thank You

Salman Khan 5 years, 2 months ago

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