Consider [math]\Delta ADC[/math] and [math]\Delta BDC[/math] . Which parts of these two triangles are equal (based on what is shown here)? Do you think these triangles are congruent?[br][br](Scroll down for more questions when you have answered this part.)

[br][br][br][br][br]Now, drag the point D (if you have not done so).[br][br]Answer again the previous questions:[br](a) which parts of these triangles are equal?[br](b) are these triangle congruent?[br][br]Have you changed your answers? Why?