Use the first few given points
for (0,-4) : -4 = 0 + 0 - 4 , nothing new learned here
for (1,0) : 0 = a + b - 4 ----> a+b+4 or b = 4-a
for (2,2) : 2 = 4a + 2b - 4 --- 2a + b = 3
use substitution
2a + (4-a) = 3
a = -1
then b = 4-(=1) = 5
y = -x^2 + 5x - 4
test if the other points satisfy, they do!
y= ax^2+bx-4. How would i find the equation of this parabola with the points (0,-4) (1,0) (2,2) (4,0) and 6,-10)?
3 answers
You must write equation for any pair of points.
y=ax^2+bx-4
x=0 y= -4
-4=a*0^2+b*0+c
0+0+c= -4
c= -4
x=1 y=0
0=a*1^2+b*1-4
a*1+b*1-4=0
a+b-4=0
a=4-b
x=2 y=2
y=ax^2+bx-4
2=(4-b)*2^2+b*2-4
(4-b)*4+2b-4=2
16-4b+2b=2+4
-2b=6-16
-2b= -1 Divide with -2
b=5
a=4-b
a=4-5
a= -1
So:
a= -1 b=5 c= -4
y=ax^2+bx+c= -x^2+5x-4
y=-x^2+5x-4
Checking of results:
For x=4
y=ax^2+bx-4
y= -4^2+5*4-4
y= -16+20-4
y=4-4
y=0
Correct value
For x=6
y=ax^2+bx-4
y= -6^2+6*5-4
y= -36+30-4
y= -6-4
y= -10
Correct value
y=ax^2+bx-4
x=0 y= -4
-4=a*0^2+b*0+c
0+0+c= -4
c= -4
x=1 y=0
0=a*1^2+b*1-4
a*1+b*1-4=0
a+b-4=0
a=4-b
x=2 y=2
y=ax^2+bx-4
2=(4-b)*2^2+b*2-4
(4-b)*4+2b-4=2
16-4b+2b=2+4
-2b=6-16
-2b= -1 Divide with -2
b=5
a=4-b
a=4-5
a= -1
So:
a= -1 b=5 c= -4
y=ax^2+bx+c= -x^2+5x-4
y=-x^2+5x-4
Checking of results:
For x=4
y=ax^2+bx-4
y= -4^2+5*4-4
y= -16+20-4
y=4-4
y=0
Correct value
For x=6
y=ax^2+bx-4
y= -6^2+6*5-4
y= -36+30-4
y= -6-4
y= -10
Correct value
I make one mistake in typig.
-2b= -1 Divide with -2 is mistake
-2b= -10 Divide with -2 is correct
-2b= -1 Divide with -2 is mistake
-2b= -10 Divide with -2 is correct