Exercise 18 Page 61

We want to draw the graph of the given quadratic function. To do so, we will rewrite it in vertex form, f(x)=a(x-h)^2+k, where a, h, and k are either positive or negative numbers. y=(x-2)^2-1 ⇕ y=1(x-2)^2+(-1) To draw the graph, we will follow four steps.

1. Identify the constants a, h, and k.
2. Plot the vertex (h,k) and draw the axis of symmetry x=h.
3. Plot any point on the curve and its reflection across the axis of symmetry.
4. Sketch the curve.

   Let's get started.

   Step 1

   We will first identify the constants a, h, and k. Recall that if a<0, the parabola will open downwards. Conversely, if a>0, the parabola will open upwards. Vertex Form:& f(x)= a(x- h)^2+k Function:& y= 1(x- 2)^2+(- 1) We can see that a= 1, h= 2, and k=- 1. Since a is greater than 0, the parabola will open upwards.

   Step 2

   Let's now plot the vertex ( h,k) and draw the axis of symmetry x= h. Since we already know the values of h and k, we know that the vertex is ( 2,- 1). Therefore, the axis of symmetry is the vertical line x= 2.

   

   Step 3

   We will now plot a point on the curve by choosing an x-value and calculating its corresponding y-value. Let's try x=4.
   y=(x-2)^2-1

   Substitute

   x= 4

   y=( 4-2)^2-1

   ▼

   Simplify right-hand side

   SubTerm

   Subtract term

   y=(2)^2-1

   CalcPow

   Calculate power

   y=4-1

   SubTerm

   Subtract term

   y=3
   When x=4, we have y=3. Thus, the point (4,3) lies on the curve. Let's plot this point and reflect it across the axis of symmetry.
   

   Note that both points have the same y-coordinate.

   Step 4

   Finally, we will sketch the parabola which passes through the three points. Remember not to use a straightedge for this!