Hello0, Jeuk!

Your work is great . . . Thank you for showing it!

Find a formula for: .

We crank out the first few partial sums:

. .

We conjecture that the formula is of the form: .

Then I stack the equations (in reverse order):

. .

There is a nice "rhythm" for solving this system of equations.

I hope you can catch on to the pattern . . .

Substitute into [14]: .

Substitute into [12]: .

Substitute into [9]: .

Substitute into [1]: .

Hence: .

. . Therefore: .