Cracking The Ap Calculus ab Exam 2018

(Marvins-Underground-K-12) #1
(−1,    0)  into    the second  equation,   we  get 0   =   c(−1)   +   (−1)^2 ,    which   simplifies  to  c   =   1.  Now we

can find    the values  for a,  b,  and c.  We  get a   =   1,  b   =   0,  and c   =   1.

SOLUTIONS TO PRACTICE PROBLEM SET 9



  1. c = 0


The  Mean    Value   Theorem     says    that:   If f(x)     is  continuous  on  the     interval    [a,    b]   and     is

differentiable  everywhere  on  the interval    (a, b), then    there   exists  at  least   one number  c   on  the

interval    (a, b)  such    that    f′(c)   =    .  Here,   the function    is  f(x)    =   3x^2    +   5x  −   2   and the

interval     is  [−1,    1].     Thus,   the     Mean    Value   Theorem     says    that    f′(c)   =  

. This simplifies to f′(c) = 5. Next, we need to find f′(c). The


derivative  of  f(x)    is  f′(x)   =   6x  +   5,  so  f′(c)   =   6c  +   5.  Now,    we  can solve   for c:  6c  +   5   =   5   and c

=   0.  Note    that    0   is  in  the interval    (−1,    1), just    as  we  expected.


  1. c =


The  Mean    Value   Theorem     says    that:   If f(x)     is  continuous  on  the     interval    [a,    b]   and     is

differentiable  everywhere  on  the interval    (a, b), then    there   exists  at  least   one number  c   on  the

interval    (a, b)  such    that    f′(c)   =    .  Here    the function    is  f(x)    =   x^3     +   24x −   16  and the

interval     is  [0,     4].     Thus,   the     Mean    Value   Theorem     says    that    f′(c)   =  

. This simplifies to f′(c) = 40. Next, we need to find f′(c) from


the equation.   The derivative  of  f(x)    is  f′(x)   =   3x^2    +   24, so  f′(c)   =   3c^2    +   24. Now,    we  can solve

for c:  3c^2    +   24  =   40  and c   =   ± . Note    that        is  in  the interval    (0, 4), but −   is  not in  the

interval.   Thus,   the answer  is  only    c   =    .  It’s    very    important   to  check   that    the answers you get

for c   fall    in  the given   interval    when    doing   Mean    Value   Theorem problems.
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