Write out the last two terms of the summation on the left side,
and write out the first two terms on the right side:



Subtract  from both sides:







2.6868299... × 10-125 = 1.75

That's certainly false!

Edwin

   1000 
  (sigma) 7(3/4)^n  =
   n=2

      1000
   7*(sigma) (3/4)^n  =    [move the constant 7 outside the summation symbol]
      n=2

               1000
   (7(3/4)^2)*(sigma) (3/4)^(n-2)  =    [move 2 powers of (3/4) outside the summation symbol]
               n=2

            998
   (63/16)*(sigma) (3/4)^n    [redefine the index]
            n=0