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CBSE Class 10 Answered

A.P.series
Asked by | 27 Oct, 2013, 11:29: PM
answered-by-expert Expert Answer

-4 + (-1) + 2 + …. + x = 437

The formula for Arithmetic Progression is given by: ak = a1 + (k - 1)d
where d = - 1 - (-4) = - 1 + 4 = 3

a1 = -4, d = 3
Hence, ak = -4 + (n - 1)3 è an = 3n - 7

We know that Sn =  (a1 + an) è Sn =  (-4 + 3n - 7)
or 437 x 2 = n (3n - 11)
On solving for ‘n’, we get: n = 295

Answered by | 28 Oct, 2013, 09:54: AM

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