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## Pixar in a Box

### Course: Pixar in a Box>Unit 11

Lesson 2: Calculating parabolas

# 4. How can we prove this?

Okay we know how to calculate the touching point, great! Next let's think about how we can prove this is true.

## Want to join the conversation?

• I agree that as s->t the intersection point get closer to parabola, but I don't get why when s=t that point lies exactly on parabola. How can intersection of two identically line segments be single point. Am I missing something here?
• As s -> t (but not s=t) the point seems to get closer &closer to the parabola. So we 'assume' that if s is infinitely close to t the point almost lies on the parabola. Notice that in the video the s line doesn't coincide with the t line cause then it won't have a specific intersection point.
Hope this helps. :)
• Actually, I don't get the meaning of proving the formula is true. It means it is true to describe the movement of the touching point by this formula?
• Yes, the point of the proof is to show that if you have a line that starts at a point, Q, which is t along AB, and ends at a point, R, which is t along BC, then it touches the parabola at a point that is t along line QR.
• Is this connected to the Bezier Curves?
(1 vote)
• I don't get this app can someone help me?
(1 vote)
• how can get a full note on the algebra because sometimes i get confused
(1 vote)
• in what does "S" stand for and also what does "T" stand for?
(1 vote)
• What is the formula? Is it the same ones from the last video and practice?
(1 vote)
• Are two lines that stay on top of each other considered to be intersect?