Graph of quadratic function:

1. GRAPH OF QUADRATIC
FUNCTION
NADEEM UDDIN
ASSOCIATE PROFESSOR
OF STATISTICS
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2. * Graph of quadratic function:
The graph of a quadratic equation is always a curve called
parabola, as given below in the solution of example. In order
to draw a better graph of quadratic equation it is necessary
for us to assign at least 7 symmetrical values of x and their
corresponding value of y.
The graph may be upward or downward opening with a
turning point called vertex.
The procedure is explained in the following example.
Example
Draw a graph of the function y = x2- 2x - 9.

3. Solution:
First of all we assign different values to ‘x’ and obtain
the values of ‘y’.
Let x = -4, -3, -2, -1, 0, 1, 2, 3, 4, 5
x y = x2 - 2x – 9 Y (x, y)
-4 y = (-4)2 -2(-4)–9 = 16+8-9 = 15 15 (-4, 15)
-3 y = (-3)2 -2(-3)–9 = 9+6-9 = 6 6 (-3, 6)
-2 y = (-2)2 -2(-2)–9 = 4+4-9 = -1 -1 (-2, -1)
-1 y = (-1)2 -2(-1)–9 = 1+2-9 = -6 -6 (-1, -6)
0 y = (0)2 -2(0)–9 = 0+0-9 = -9 -9 (0, -9)
1 y = (1)2 -2(1)–9 = 1-2-9 = -10 -10 (1, -10)
2 y = (2)2 -2(2)–9 = 4-4-9 = -9 -9 (2, -9)
3 y = (3)2 -2(3)–9 = 9-6-9 = -6 -6 (3, -6)
4 y = (4)2 -2(4)–9 = 16-8-9 = -1 -1 (4, -1)
5 y = (5)2 -2(5)–9 = 25-10-9 = 6 6 (5, 6)

4. Now we plot the points
The graph of quadratic equation may also be rightward or leftward opening.