If the maximum value of f(x) is 20, then what is the maximum value of (2x - 10) if f(x) = -4x^2+ bx + c?

The maximum value of (2·x - 10) is 20

Step-by-step explanation:

Given that the maximum value of f(x) = 20

f(x) = -4·x² + bx + c

We are required to find the maximum value of (2·x - 10)

f'(x) = -8·x + b = 0

x = b/8

f''(x) = -8, therefore, f'(x) is the maximum point

20 = -4·x² +8·x²  + c

20 = -4·(b/8)² + b×(b/8) + c

20 = -b²/16 + b²/8 + c

20 = b²/16 + c

f(2·x - 10) = -4·(2·x - 10)² + b·(2·x - 10) + c

f(2·x - 10) = b·(2·x - 10) + c - (16·x²-160·x +400

Differentiating to find the maximum gives;

f'(2·x - 10) = d(b·(2·x - 10) + c - (16·x²-160·x +400)/dx = 2·b -32·x +160 = 0

x = (2·b +160)/32 = 0.0625·b +5

At the maximum point, therefore, we have;

b·(2·(0.0625·b +5) - 10) + c - (16·(0.0625·b +5)²-160·(0.0625·b +5) +400

At the max value of f(2·x - 10) = b²/16 + c

Since b²/16 + c = 20, we have the maximum value of (2·x - 10) = 20.

use an equation of ratios to determine the amount of gas needed to fill the tank.

    0.2             0.8

  =    

288.75             x

                                                              231 gal

so, 0.2x = (0.8)(288.75 gal), and x = = 1155 gal.

                                                                0.2

it would take 1155 gal. to fill the tank.

the cost would be

1155 gal         $3

* = $3465   (answer)

      1           1 gal

hope this you