Question

(1/t-1)-(1/t+2)

Answer 1

As it is, the answer is

(1/t-1)-(1/t+2)
= 1/t-1-1/t-2
= -3

If I suppose that some parentheses are missing, then it requires finding a common denominator:
1/(t-1)-1/(t+2)
= ((t+2) - (t-1))/((t-1)(t+2))
= 3/((t-1)(t+2))