SOLUTION: give an example of polynomials p and q of degree 3 such that p(1)=q(1), p(2)=q(2), p(3)=q(3), but p(4) =(not equal) q(4). Show that your polynomials satisfy these conditions.

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: give an example of polynomials p and q of degree 3 such that p(1)=q(1), p(2)=q(2), p(3)=q(3), but p(4) =(not equal) q(4). Show that your polynomials satisfy these conditions.       Log On


   



Question 577369: give an example of polynomials p and q of degree 3 such that p(1)=q(1), p(2)=q(2), p(3)=q(3), but p(4) =(not equal) q(4). Show that your polynomials satisfy these conditions.
Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!
There is probably a very simple and elegant solution, but I will only see it after I post this messy one,
Consider the function f%28x%29=p%28x%29-q%28x%29
f%281%29=p%281%29-q%281%29=0
f%282%29=p%282%29-q%282%29=0
f%283%29=p%283%29-q%283%29=0
There are two many options, but I would try the simplest polynomial function with those three zeros:

I can split f%28x%29 into p%28x%29 and -q%28x%29 many ways, but I need both polynomials to be of degree 3.
I'll try something. There are probably better, simpler ways.
p%28x%29=2x%5E3-2x%5E2%2B2x-2=2%28x%5E3-x%5E2%2Bx-1%29 and
-q%28x%29=-x%5E3-4x%5E2%2B9x-4 made up so that p%28x%29%2B%28-q%28x%29%29=p%28x%29-q%28x%29=x%5E3-6x%5E2%2B11x-6
q%28x%29=x%5E3%2B4x%5E2-9x%2B4
Polynomials p and q are of degree 3
p%281%29=2%281%5E3-1%5E2%2B1-1%29=0 and q%281%29=1%5E3%2B4%2A1%5E2-9%2A1%2B4=1%2B4-9%2B4=0, so p%281%29=q%281%29
p%282%29=2%282%5E3-2%5E2%2B2-1%29=2%288-4%2B2-1%29=2%2A5-10 and q%282%29=2%5E3%2B4%2A2%5E2-9%2A2%2B4=8%2B4%2A4-18%2B4=8%2B16-18%2B4=10, so p%282%29=q%282%29
p%283%29=2%283%5E3-3%5E2%2B3-1%29=2%2827-9%2B3-1%29=2%2A20=40 and q%283%29=3%5E3%2B4%2A3%5E2-9%2A3%2B4=27%2B4%2A9-27%2B4=27%2B36-27%2B4=40, so p%283%29=q%283%29
I should not have to prove that, brcause there could only be 3 intersection points for two polynomials of degree 3, but ...
p%284%29=2%284%5E3-4%5E2%2B4-1%29=2%2864-16%2B4-1%29=2%2A51=102 and q%284%29=4%5E3%2B4%2A4%5E2-9%2A4%2B4=64%2B64-36%2B4=128-36%2B4=96, so p%284%29 and q%284%29 are different.