Question

What is the maximum value of -4z^2+20z-6?

Answer 1

Answer:

Hello,

19

Step-by-step explanation:

2 methodes:

1)

$y=-4x^2+20x-6\\\\=-4(x^2-5x)-6\\\\=-4(x^2-2*\dfrac{5}{2}*x+\dfrac{25}{4} ) +25-6\\\\=-4(x-\frac{5}{2} )^2+19\\\\Maximum\ =19 \ if\ x=\dfrac{5}{2}$

2)

y'=-8x+20=0 ==> x=20/8=5/2

and y=-4*(5/2)²+20*5/2-6=-25+50-6=19

Answer 2

Answer:

The maximum value is 19

Step-by-step explanation:

We want to find the maximum value of:

y = -4z^2+20z-6

Here, you can see that we have a quadratic with a negative leading coefficient.

This means that the arms of the graph will go downwards. From this, we can conclude that the maximum will the at the vertex (the highest point).

Remember that for a general equation like:

y = a*x^2 + b*x + c

The x-value of the vertex is:

x = -b/(2a)

(you can see that the variable is a different letter, that does not matter, is just notation)

Then for our equation:

y = -4z^2+20z-6

The z-value of the vertex is:

z = -20/(2*-4) = -20/-8 = 5/2

Then the maximum of the equation:

y = -4z^2+20z-6

is that equation evaluated in z = 5/2

So we get:

y = -4*(5/2)^2 + 20*(5/2) - 6  = 19

The maximum value is 19