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Rammstein53
11 months ago

The cross-sectional area is in cm: (40 – 2x)*x

This should result in 150: (40 – 2x)*x = 150

-2×2 + 40*x – 150 = 0

The square equation has two solutions: x = 5 and x = 15

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The cross-sectional area (40 – 2x)*x should be maximum.

f(x) = -2×2 + 40x

f'(x) = -4x + 40

f”'(x) = -4

f'(x) = 0 for x = 10 cm

This is a maximum because f”(10) < 0

MichaelH77
11 months ago

A is the rectangular cross-sectional area, i.e. A=(b-2x)*x

MichaelH77
11 months ago
Reply to  Claudschi007

width b is given

the first part is also given A, then you can calculate x directly

do not forget to convert the mm into cm

first multiply in the second part, then the square equation is converted into a crown form by quadratic supplementing, then it is known for which x value the surface A becomes maximum

-2*[(x-100)2-1002] = A