
Concept explainers
To prove: the x -coordinate of the vertex of the graph is the average of the zeros of
f(x)=ax2+bx+c , a≠0 .

Explanation of Solution
Concept Used:
For the function f(x)=ax2+bx+c with vertex (−b2a,f(−b2a)) ,
- When a>0 , f has a minimum at x=−b2a and the minimum value is f(−b2a) .
- When a<0 , f has a maximum at x=−b2a and the maximum value is f(−b2a) .
From the above definition it is clear that the x -coordinate of the vertex of the graph is equal to −b2a .
Now to show the x coordinate of the vertex is equal to average of the zeros of f(x)=ax2+bx+c
Using quadratic equation to find zeros of the equation ax2+bx+c=0 ,
x=−b±√b2−4ac2a
SO, the two zeros of the equation ax2+bx+c=0 are:
x1=−b+√b2−4ac2a And x2=−b√b2−4ac2a
Now find average of these zeros.
x1+x22=−b+√b2−4ac2a+−b−√b2−4ac2a2=−b+√b2−4ac−b−√b2−4ac4a=−2b4a=−b2a
Hence proved that, the x -coordinate of the vertex of the graph is the average of the zeros of
f(x)=ax2+bx+c , a≠0 .
Chapter 2 Solutions
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