How to Draw a Graph of a Quadratic Function by Novi Handayani

     1. For example, we have y = x²  + 4x + 4

              2. Remember the basic form for quadratic function is ax²  + bx + c then, we can remember if the value of a   positive then it has right side up so it has minimum point if the value of a is negative then it has upside down so it has maximum point

         3. In this case we have minimum point (vertex)

  .      4. First, find the vertex of function above, by using -b / 2a   to find point x in vertex. 

                 5. Then, to find the value of y in vertex we can substitute the value of x, for example :

      x = -b / 2a   = -4 / 2(1) = -2

      then, y = x²  + 4x + 4

              y = (-2)² + 4(-2) +4

              y = 4 – 8 + 4

               y = 0

so, the vertex is (-2,0)

6. Then, we can find the additional point to make us easier to sketch the graph

For this case,

Point substitute	(-2)2 + 4(-2) +4	Result
-7	(-7)2 + 4(-7) +4	25
-6	(-6)2 + 4(-6) +4	16
-5	(-5)2 + 4(-5) +4	9
-4	(-4)2 + 4(-4) +4	4
-3	(-3)2 + 4(-3) +4	1
-2	(-2)2 + 4(-2) +4	0
-1	(-1)2 + 4(-1) +4	1
0	(0)2 + 4(0) +4	4
1	(1)2 + 4(1) +4	9
2	(2)2 + 4(2) +4	16
3	(3)2 + 4(3) +4	25