When should we use the method of substituting x = a + h in right hand limit and x = a-h in left hand limit while solving problems in limits ?
When a function h -LRB- x -RRB- is bounded , how do I prove that the limit of -LSB- f -LRB- x -RRB- * h -LRB- x -RRB- -RSB- as x - > a equals zero ?