Given:
The function is:
[tex]f(x)=-2x^2+7x+4[/tex]
To find:
Express the quadratic equation in the form of [tex]f(x)=a(x-h)^2+k[/tex], then state the minimum or maximum value,axis of symmetry and minimum or maximum point.
Solution:
The vertex form of a quadratic function is:
[tex]f(x)=a(x-h)^2+k[/tex] ...(i)
Where, a is a constant, (h,k) is the vertex and x=h is the axis of symmetry.
We have,
[tex]f(x)=-2x^2+7x+4[/tex]
It can be written as:
[tex]f(x)=-2\left(x^2-3.5x\right)+4[/tex]
Adding and subtracting square of half of coefficient of x inside the parenthesis, we get
[tex]f(x)=-2\left(x^2-3.5x+(\dfrac{3.5}{2})^2-(\dfrac{3.5}{2})^2\right)+4[/tex]
[tex]f(x)=-2\left(x^2-3.5x+(1.75)^2\right)-2\left(-(1.75)^2\right)+4[/tex]
[tex]f(x)=-2\left(x-1.75\right)^2+2(3.0625)+4[/tex]
[tex]f(x)=-2\left(x-1.75\right)^2+6.125+4[/tex]
[tex]f(x)=-2\left(x-1.75\right)^2+10.125[/tex] ...(ii)
On comparing (i) and (ii), we get
[tex]a=-2,h=1.75,k=10.125[/tex]
Here, a is negative, the given function represents a downward parabola and its vertex is the point of maxima.
Maximum value = 10.125
Axis of symmetry : [tex]x=1.75[/tex]
Maximum point = (1.75,10.125)
Therefore, the vertex form of the given function is [tex]f(x)=-2\left(x-1.75\right)^2+10.125[/tex], the maximum value is 10.125, the axis of symmetry is [tex]x=1.75[/tex] and the maximum point is (1.75,10.125).
