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What is the equation of the parabola passing through (1,5), (0,6), and (2,3)?

 Apr 14, 2017
 #1
avatar+15062 
0

What is the equation of the parabola passing through (1.5), (0.6), and (2,3)?


Is it a parable of 2 or 3 potency?
Also a circle cuts the three points.

 Apr 14, 2017
 #2
avatar+130466 
+2

(1,5), (0,6), and (2,3)

 

We have this form

 

y = a(x - h)^2  + k       where "a" determines the width (and direction - "up" or "down" ) of the parabola, and (h,k) is the vertex

 

So  we know that

 

5  =  a ( 1 - h)^2 + k     →  5 = a(1 -2h + h^2) + k  →  5 = a -2ah + ah^2 + k   (1)

6  = a(0 - h)^2 + k  →  6 = ah^2 + k   (2)

3 = a(2 - h)^2 + k   →  3 = a(4 - 4h + h^2) + k → 3 =  4a -4ah +ah^2 + k     (3) 

 

Sub ( 2) into  (1)  and (3)

 

5 =  a - 2ah + 6     →  -1  =  a - 2ah   ( 4)

3  = 4a - 4ah + 6  →  -3 = 4a - 4ah     (5)

 

Multiply  (4) by -2 and add it to (5)

 

-1  =  2a    →  a  = -1/2

 

Using (4)  to find h, we have

 

-1 = (-1/2) - 2 (-1/2)h

-1/2  =  h

 

Using (2)  to find k, we have

 

 6 = (-1/2)(1/4) + k

 

k = 6 + 1/8  =  49/8

 

So..........our equation is

 

y = (-1/2)(x + 1/2)^2 + 49/8

 

Here's the graph with the points of interest  : https://www.desmos.com/calculator/vnyrl52lp8

 

 

cool cool cool

 Apr 14, 2017
 #3
avatar+26396 
+1

What is the equation of the parabola passing through (1,5), (0,6), and (2,3)?

 

Formula parabola:

y=ax2+bx+c

 

a, b, c = ?

P(0,6):6=02a+0b+c6=cP(1,5):5=12a+1b+c5=a+b+c|c=6(1)5=a+b+6P(2,3):3=22a+2b+c3=4a+2b+c|c=6(2)3=4a+2b+6

 

a, b = ?

(2)3=4a+2b+6|:21.5=2a+b+3(1)5=a+b+6(2)(1):1.55=2a+b+3(a+b+6)3.5=2a+b+3ab63.5=a30.5=a5=a+b+6|a=0.55=0.5+b+65=5.5+b55.5=b0.5=b

 

Formula parabola:

y=ax2+bx+c|a=0.5b=0.5c=6y=0.5x20.5x+6

 

laugh

 Apr 18, 2017

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