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  1. Home
  2. 12th grade
  3. Algebra II
  4. Exercise : Find properties of a parabola from equations

Find properties of a parabola from equations Algebra II

Determine the vertex of the following parabola:

y=2\left(x-1\right)^2+1

When a parabola is given in the vertex form:

y=a\left(x-h\right)^2+k

The vertex of a parabola is \left(h,k\right).

Here, we have:

y=2\left(x-1\right)^2+1

The vertex of the parabola is (1,1).

Determine the focus of the following parabola:

y=\left(x-2\right)^2+3

When a parabola is given in the vertex form:

y=a\left(x-h\right)^2+k

The vertex of a parabola is \left(h,k\right) and the focus is \left(h,k+\dfrac{1}{4a}\right).

Here, we have:

  • \left(h,k\right)=\left(2{,}3\right)
  • F=\left(2{,}3+\dfrac{1}{4}\right)=\left(2,\dfrac{13}{4}\right)

The focus of the parabola is \left(2,\dfrac{13}{4}\right).

Determine the focus of the following parabola:

x=\dfrac{1}{2}\left(y+1\right)^2+2

When a parabola is given in the vertex form:

x=a\left(y-k\right)^2+h

The vertex of a parabola is \left(h,k\right) and the focus is \left(h+\dfrac{1}{4a},k\right).

Here, we have:

  • \left(h,k\right)=\left(2,-1\right)
  • F=\left(2+\dfrac{1}{\left(4\times \dfrac{1}{2}\right)},-1\right)=\left(2+\dfrac{1}{2},-1\right)=\left(\dfrac{5}{2},-1\right)

The focus of the parabola is \left(\dfrac{5}{2},-1\right).

Determine the vertex of the following parabola:

x=y^2+6y+10

When a parabola is given in the vertex form:

x=a\left(y-k\right)^2+h

The vertex of a parabola is \left(h,k\right). Find the vertex form of the parabola:

x=y^2+6y+10

x=\left(y^2+6y+9\right)+1

x=\left(y+3\right)^2+1

Therefore:

The vertex of the parabola is (1,-3).

Determine the vertex of the following parabola:

y=2x^2+16x+40

When a parabola is given in the vertex form:

y=a\left(x-h\right)^2+k

The vertex of a parabola is \left(h,k\right). Find the vertex form of the parabola:

Here we have:

y=2x^2+16x+40

y=2\left(x^2+8x+ 16\right)+8

y=2\left(x+4\right)^2+8

The vertex of the parabola is (-4,8).

Determine the focus of the following parabola:

y=x^2+4x+5

When a parabola is given in the vertex form:

y=a\left(x-h\right)^2+k

The vertex of a parabola is \left(h,k\right) and the focus is \left(h,k+\dfrac{1}{4a}\right). Find the vertex form of the parabola:

y=x^2+4x+5

y=\left(x^2+4x+4\right)+1

y=\left(x+2\right)^2+1

So we have:

  • \left(h,k\right)=\left(-2{,}1\right)
  • F=\left(-2{,}1+\dfrac{1}{4}\right)=\left(-2,\dfrac{5}{4}\right)

The focus of the parabola is \left(-2,\dfrac{5}{4}\right).

Determine the focus of the following parabola:

x=y^2+6y+12

When a parabola is given in the vertex form:

x=a\left(y-k\right)^2+h

The vertex of a parabola is \left(h,k\right) and the focus is \left(h+\dfrac{1}{4a},k\right). Find the vertex form of the parabola:

x=y^2+9x+12

x=\left(y^2+6y+9\right)+3

x=\left(y+3\right)^2+3

So we have:

  • \left(h,k\right)=\left(3,-3\right)
  • F=\left(3+\dfrac{1}{4},-3\right)=\left(\dfrac{13}{4},-3\right)

The focus of the parabola is \left(\dfrac{13}{4},-3\right).

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See also
  • Course : Parabolas
  • Exercise : Write equations of parabolas from properties
  • Exercise : Write equations of parabolas from graphs
  • Exercise : Convert equations of parabolas from general to vertex form
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