Question

the sum of n terms of anAP whose first term is 6 and common difference is 40 is equal to the sum of 2n terms of another AP whose first term is 40 and common difference is 6 find. n​

Answer 1

Answer:

mrk brainliest plsss

Step-by-step explanation:

For 1st series

1st term = 6

common difference=40

now ,

sum of n terms (Sn) =n/2{2a + (n-1)d}

Sn =n/2{2 × 6 +(n-1) 40}

=n( 6 +20n -20)

=n(20n-14)

for 2nd series ,

first term = 40

common difference =6

S(2n) =2n/2{2 × 40 +(2n -1)6}

=n {80 +12n -6}

=n {74 +12n}

a/c to question,

Sn = S2n

n(20n -14) = n(74 + 12n)

20n -14 = 74 + 12n

8n =88

n=11