Evaluate `7+ 77+777+......`upto `n`

prove that 7 + 77 + 777 +...... + 777........._(n-digits) 7 = 7/81 (10^(n+1) - 9n - 10) for all n in N

Sum of the series 1+3+7+15+....... upto n terms.

777:1147

If (1 + 3 + 5 + .... " upto n terms ")/(4 + 7 + 10 + ... " upto n terms") = (20)/(7 " log"_(10)x) and n = log_(10)x + log_(10) x^((1)/(2)) + log_(10) x^((1)/(4)) + log_(10) x^((1)/(8)) + ... + oo , then x is equal to

Find the sum of the sequence 7,77,777,7777... to n terms.

The sum of 10 terms of the series 0.7+0.77+0.777+....... is

Find the sum of the series : (i) 8+88+888+ ... to n terms (ii) 3+33+333+ ... to n terms (iii) 0.7+0.77+0.777+ ... to n terms

The sum of first 20 terms of the sequence 0.7, 0.77, 0.777, .. , is (1) 7/9(99-10^(-20)) (2) 7/(81)(179+10^(-20)) (3) 7/9(99+10^(-20)) (3) 7/(81)(179-10^(-20))

Prove 1.4.7+2.5.8+3.6.9+....... upto n terms =(n)/(4)(n+1)(n+6)(n+7)