Just to expand on OTPMs answer- if task 3 has 2 dependencies, then it is really 2 tasks not one. I would suggest linking task 1 to task 3a, taks 2 to 3b, and then linking 3a to 3b (assuming the second half needs the first part to be completed before it can be carried out).

This assumes that the tasks are not resource driven (i.e. that 2 different people are carrying out both 1 and 2, and are both needed to do task 3), which is a different scenario.