Hello!
We have the function below:
[tex]h\mleft(x\mright)=-2x^2+5x-8[/tex]
The first step is to identify the coefficients a, b and c:
• a = -2
,
• b = 5
,
• c = -8
Just by analyzing these coefficients, we can say that the concavity of the parabola will be facing downwards because the coefficient a is negative
1st step: using the quadratic formula, we will find the interceptions in the x-axis. Look:
[tex]x=\frac{-b\pm\sqrt[]{b^2-4\cdot a\cdot c}}{2\cdot a}[/tex]
As we know the coefficients, let's replace them in the formula:
[tex]\begin{gathered} x=\frac{-5\pm\sqrt[]{5^2-4\cdot(-2)\cdot(-8)}}{2\cdot(-2)} \\ \\ x=\frac{-5\pm\sqrt[]{25^{}-64}}{-4}=\frac{-5\pm\sqrt[]{-39}}{-4}= \end{gathered}[/tex]
Obs: as we obtained a negative square root, we can stop this step here. It means that
2nd step: let's identify the maximum point of it:
[tex]\begin{gathered} x_V=\frac{-b}{2\cdot a}=\frac{-5}{2\cdot(-2)}=\frac{-5}{-4}=1.25 \\ \\ y_V=-\frac{b^2-4\cdot a\cdot c}{4\cdot a}=-\frac{5^2-4\cdot(-2)\cdot(-8)}{4\cdot(-2)}=-\frac{-39}{-8}=-4.875 \end{gathered}[/tex]
So, the vertex is at the point (x, y) = (1.25, -4.875).
The axis of symmetry is x = 5/4 or also x = 1.25.
Look at the graph below:
Note: if you solve this function when x = 0, you will obtain one interception in the y-axis, look:
[tex]\begin{gathered} h\mleft(x\mright)=-2x^2+5x-8 \\ h\mleft(0\mright)=-2\cdot0^2+5\cdot0-8 \\ h(0)=0+0-8 \\ h(0)=-8 \end{gathered}[/tex]
So, the y-intercept is at (x, y) = (0, -8) as you can see at the graph.
