Which quadratic function has the largest maximum over the set of REAL numbers?

Both the function f(x) and g(x) have same values.
The vertex of a quadratic is the point where the graph intersects with the axis of symmetry (the line which divides the parabola in half). The vertex of a quadratic will be either a maximum or minimum.
[tex]x = \frac{-b}{2a}[/tex]
where,
b is the coefficient of x
and , a is the coefficient of [tex]x^{2}[/tex].
for, y substitute the value of x in f(x)
⇒ (x, f(x)) i.e. (x, y) will be the vertex
The minimum or maximum value of quadratic is given by the value of the function at the the vertex.
According to the given question
we have
[tex]f(x) = -x^{2} +2x+4[/tex]
and
[tex]g(x)= -(x-5)^{2} +5[/tex]
For the vertex or the function [tex]f(x)=- x^{2} +2x+4[/tex]
[tex]x =\frac{-2}{-2}[/tex] = 1
and, at x = 1
f(1) = -1+ 2+4= 5
⇒ vertex of f(x) is (1, 5)
As we know, the maximum value of y is given by y coordinate so, the maximum value of f(x) is 5 at x=1.
Similarly,
For g(x) = [tex]-(x - 5)^{2}+5 = -x^{2} -25+10x +5 =-x^{2} + 10x -20[/tex]
⇒ g(x) = [tex]-x^{2} +10x -20[/tex]
[tex]x = \frac{-10}{-2}[/tex] = 5
g(5) = -25 + 50 -20
g(5) = 5
⇒ vertex of g(x) is (5,5)
⇒ Maximum value of g(x) is 5 at x =5.
Hence, both the function have same maximum value.
Learn more about the maximum and minimum values here:
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