Question

Question 18 pg5.52 from rd sharma book 10th standard

Answer 1

Sum of terms =n/2(2a+(n-1)d)

a=4-1/n

D=4-2/n-4+1/n

-1/n

Now put these value

n/2(2*4-1/n+(n-1)-1/n

n/2(8-2/n-n/n+1/n)

n/2(7-2/n+1/n)

n/2(7-1/n)

7n/2-n/2n n/2n=1

1/2(7n-1)