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Given the following information about p(x) find a and b. Then use to find slopes in interval [0,16]?

Let p(x) be continuous and differentiable.

p(x) = 16a/sqrt(x) when x > 4

p(x) = bx^2 + 2x + 56 when x </= 4

Prove that a = and b = .

Then, using those values of a and b find the value(s) of x in the interval [0,16] at which the instantaneous slope equals the average slope.

1 Answer

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  • 8 years ago
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    To be continuous

    When x=4

    16*a/sqrt(x)=b*x^2 +2*x +56

    16*a/2=b*16+8+56

    8*a=b*16+64

    a=2*b+8

    for the differential to be continuous

    When x=4

    16*a*(-1/2)*x^(-3/2)=b*2*x+2

    -8*a/8=8*b+2

    a=-8*b-2

    subtracting the simplified equation for differentiable from the simplified equation for continuous eliminates the variable a

    a-a=2*b+8-(-8*b-2)

    0=10*b +10

    b=-1

    a=2*b+8=-2+8=6

    a=-8*b-2=8-2=6

    The average slope is not a well defined expression. I will use as my definition the sum of the instantaneous slopes at the end points divided by two.

    p'(0)=b*2*0+2=2

    p'(16)=16*a*(-1/2)*16^(-3/2)=-8*6/64=-3/4

    {p'(0)+p'(16)}/2=(2-3/4)/2=5/8

    -2*x+2=5/8

    2*x=2-5/8

    x=11/16 when the instantaneous slope is equal to the average slope over the range.

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