Given a parametric function <mtable columnalign="right left right left right left right left rig

Mohammad Cannon

Mohammad Cannon

Answered question

2022-06-24

Given a parametric function
x = x o + v x t + 1 2 a x t 2 y = y o + v y t + 1 2 a y t 2
and point P at (c,d) , find all point(s) on the function that are distance R from point P, assuming that R > 0 and none of the constants equal 0.

Answer & Explanation

mallol3i

mallol3i

Beginner2022-06-25Added 20 answers

Step 1
I'm assuming that we're given R , c , d , x 0 , v x , a x , y 0 , v y , a y .
The squared distance between P = ( c , d ) and ( x , y ) is given by
1) (1) R 2 = ( x c ) 2 + ( y d ) 2
Substitute the definition of
2) x = x 0 + v x × t + 1 2 × a x × t 2 y = y 0 + v y × t + 1 2 × a y × t 2
in (1)
You're left with a polynomial in t. Solve for t, this will give you different values of t = { t 1 , , t 4 } . . Substitute each t i in (2) to get different (x,y) points.
Step 2
I'm too lazy to LaTeX the following equation:
( 0.25 a y 2 + 0.25 a x 2 ) t 4 + ( 1.0 v y   a y + 1.0 v x   a x ) t 3 + ( v x 2 + 1.0 x o   a x 1.0 a x   c 1.0 a y   c + v y 2 + 1.0 y o   a y ) t 2 + ( 2.0 v y   c + 2.0 y o   v y + 2.0 x o   v x 2.0 v x   c ) t + x o 2 + 2.0 c 2 1.0 R 2 2.0 x o   c 2.0 y o 2 = 0
Anyways, that's the degree 4 polynomial in t. To find a closed-form expressions for the roots
{ t 1 = , t 2 = , t 3 = , t 4 = } ,
you will need to do a lot of algebra on this polynomial. For example this.

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