You will be able to tell only if all the angles are equal/the same. After this, check to make sure the lengths are in proportion (Make sure they changed by the same rate). Take the one of their lengths for the segment and divide it by the same segment length on the other triangle. This will get you the rate of change. Next, go to the first triangle you measured the length of the segment on and measure another segment and again divide the same segment line on the other triangle. Do the same for each side. If all the rates are the same, then the triangles are similar.