Question

if A1,a2,A3,..an,..are in AP such that a4-a7+A10=m,then the sum of first 13 terms of this AP is​

Answer 1

a_4 = a_1 + 3d

a_7 = a_1 + 6d

a_10 = a_1 + 9d

Given that,

a_4 - a_7 + a_10 = m

=> a_1 + 3d - (a_1 + 6d) + a_1 + 9d = m

=> a_1 + 3d - a_1 - 6d + a_1 + 9d = m

=> a_1 + 6d = m

=> a_7 = m

So we get that the 7th term is taken as m.

Now, we use the formula for sum,

S_n = n · a_((n+1)/2)

So,

S_13 = 13 · a_((13+1)/2)

S_13 = 13 · a_(14/2)

S_13 = 13 · a_7

S_13 = 13m

Hence, 13m is the answer.

Answer 2

Answer:

10m

Step-by-step explanation:

10m ok that's the answer no matter what