Explain the geometry of CCl4

We first have to know the geometry of CCl4. This should be easy: it's tetrahedral, because the carbon is bonded to four identical groups. Now, as suggested in the hint, let's do a vector addition for the bond dipoles of every Cl-C-Cl pair. (Use a dipole arrow of arbitrary length as long as it is the similar for both. We'll use an arrow with the length of the C-Cl bonds.) Here's the result of the vector addition, which we've done graphically, for the first pair. Notice that, because the C-Cl bonds are identical, the resultant must bisect the angle among the two bonds