Question

If 21st term of A.P. is 43 the. find the sum of first 41 term that of A.P.​

Answer 1

Answer:

Sum of first 41 terms of A.P is 1763

Step-by-step explanation:

Given,

21st term of A.P is 43.

a + (21 - 1)*d = 43

where, a = first term and d = common difference

a + 20d = 43 ...(i)

Now, Sum of first 41 term can be given as:

Sn = n/2 * (2a + (n-1)d)

S₄₁ = 41/2 * (2a + (41-1)d)

S₄₁ = 41/2 * (2a + 40d)

S₄₁ = 41/2 * 2(a+20d)

Substituting the value of a+20d = 43 from equation (i):

S₄₁ = 41/2 * 2*43

S₄₁ = 41 * 43

S₄₁ = 1763

Therefore, Sum of first 41 terms of A.P is 1763