well usually by convention you read from top line to bottom line:
ie. for your case, 2 - 1/k + 1/(k+1)^2 = 2 - (1/k - 1/[k(k+1)]) as they are equal not one greater than other
NOT 1 + 1/4 + 1/9... 1/k^2 + 1/(k+1)^2 = 2 - (1/k - 1/[k(k+1)])
thus the next line (in the proof) means
2 -...