SOLUTION: Find the equation of the parabola with vertex (-2,0) and y intercept 4. Can you please help me? Thanks so much in advance

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equation Customizable Word Problems -> SOLUTION: Find the equation of the parabola with vertex (-2,0) and y intercept 4. Can you please help me? Thanks so much in advance      Log On


   



Question 703935: Find the equation of the parabola with vertex (-2,0) and y intercept 4.
Can you please help me? Thanks so much in advance

Found 2 solutions by josmiceli, Edwin McCravy:
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
First write down the general form
of a parabola, which is:
+y+=+a%2Ax%5E2+%2B+b%2Ax+%2B+c+
When in this form, the x-coordinate of the vertex
is at +x%5Bv%5D+=+-b%2F%282a%29+
You are given that the vertex is at ( -2,0 ), so I can say
+-2+=+-b%2F%282a%29+
+2+=+b%2F%282a%29+
+b+=+4a+
---------------
So far, I have:
+y+=+a%2Ax%5E2+%2B+4a%2Ax+%2B+c+
The y-intercept occurs where +x+=+0+, so
+y+=+a%2A0+%2B+4a%2A0+%2B+c+
+y+=+c+
You are given that the y-intercept is +y+=+4+, so
+4+=+c+
----------------
So far, I have:
+y+=+a%2Ax%5E2+%2B+4a%2Ax+%2B+4+
Now I go back to the vertex at ( -2,0 )
+0+=+a%2A%28-2%29%5E2+%2B+4%2A%28-2%29+%2B+4+
+0+=+4a+-+8+%2B+4+
+4a+=+8+-+4+
+4a+=+4+
+a+=+1+
--------------
Now I have all I need to write the equation
+y+=+1%2Ax%5E2+%2B+4%2A1%2Ax+%2B+4+
+y+=+x%5E2+%2B+4x+%2B+4+ answer
--------------
check:
Does it go through ( 0,4) ? ( the y-intercept )
+y+=+x%5E2+%2B+4x+%2B+4+
+4+=+0%5E2+%2B+4%2A0+%2B+4+
+4+=+4+
OK
Here's the plot:
+graph%28+400%2C+400%2C+-6%2C+6%2C+-6%2C+10%2C+x%5E2+%2B+4x+%2B+4+%29+

Answer by Edwin McCravy(20054) About Me  (Show Source):
You can put this solution on YOUR website!
Find the equation of the parabola with vertex (-2,0) and y intercept 4
graph%28400%2C240%2C-10%2C10%2C-2%2C10%2C%28x%2B2%29%5E2%29
y = a(x-h)² + k
Substitute (h,k) = (-2,0) and (x,y) = (0,4)
4 = a(0-(-2))² + 0
4 = a(2)²
4 = 4a
1 = a
Substitute for just a, h and k, not x or y
y = a(x-h)² + k
y = 1(x-(-2))² + 0
y = (x+2)²
Or you can multiply that out
y = x²+4x+4