SOLUTION: what can a and k be so both points are on the graph of function? points are (1,11) and (2,-19); function is y= a(x+1)^2 + k how can i find the function so that both poitns are on

Algebra ->  Quadratic Equations and Parabolas -> SOLUTION: what can a and k be so both points are on the graph of function? points are (1,11) and (2,-19); function is y= a(x+1)^2 + k how can i find the function so that both poitns are on      Log On


   



Question 105257This question is from textbook
: what can a and k be so both points are on the graph of function?
points are (1,11) and (2,-19); function is y= a(x+1)^2 + k
how can i find the function so that both poitns are on the graph??
This question is from textbook

Answer by Earlsdon(6294) About Me  (Show Source):
You can put this solution on YOUR website!
One way to do these is to substitute the x- and y-values from the given points into the equation, thus giving you a system of equations with two unknowns (a and k). Then solve the system of equations for the two unknowns.
y+=+a%28x%2B1%29%5E2%2Bk Substitute x = 1 and y = 11 from the first point (1, 11) to get the first equation.
11+=+a%281%2B1%29%5E2%2Bk Simplify.
11+=+4a%2Bk
Second equation:
y+=+a%28x%2B1%29%5E2%2Bk Substitute the x- and y-values from the second point (2, -19) to get the second equation:
-19+=+a%282%2B1%29%5E2%2Bk Simplify.
-19+=+9a%2Bk
So now you have the two equatios:
1) 11+=+4a%2Bk and
2) -19+=+9a%2Bk You can solve these by any of the accepted methods for solving systems of equations. Let's use elimination by subtracting equation 1) from equation 2) and solving for a.
-30+=+5a Divide both sides by 5.
a+=+-6 Now substitute this value of a into either equation 1) or equation 2) and solve for k. Let's use equation 1)
11+=+4a%2Bk Substitute a = -6
11+=+4%28-6%29%2Bk
11+=+-24%2Bk Add 24 to both sides.
k+=+35
Check: Into the original equation, substitute a = -6 and k = 35.
y+=+-6%28x%2B1%29%5E2%2B35
Now let's see if the two given points (1, 11) and (2, -19) satisfy this equation.
11+=+-6%281%2B1%29%5E2%2B35
11+=+-6%284%29%2B35
11+=+-24%2B35
11+=+11 Ok for the first point.
-19+=+-6%282%2B1%29%5E2%2B35
-19+=+-6%289%29%2B35
-19+=+-54%2B35
-19+=+-19 Ok for the second point.