What is 4 -4 + infinity - infinity As x approaches 3 from the right (i.e. 3) the values are just bigger that 3. So the denominator is positive and approaching 0. Hence the limit is going to + infinity. Had the denominator been (3 - x) then the answer would have been - infinity. Solution c) +infinity if x approaches from 3+ then it will always be less than 3 ,suppose x=3.00001 then the difference = 3-3.00001 = -.00001 hence when denominator is 3-x it will always tend to (-infinity).