Cracking The Ap Calculus ab Exam 2018

(Marvins-Underground-K-12) #1
point   (4, 7).

Next,    we  take    the     derivative:     =   .   Now,    we  can     find    the

slope,  m:      =   −6. However,    this    is  the slope   of  the tangent line.   The normal

line    is  perpendicular   to  the tangent line,   so  its slope   will    be  the negative    reciprocal  of  the

tangent line’s  slope.  In  this    case,   the slope   of  the normal  line    is   .  Finally,    we  plug    in  the

point   (4, 7)  and the slope   m   =       to  get the equation    of  the normal  line:   y   −   7   =    (x −   4).


  1. y = 0


Remember    that    the equation    of  a   line    through a   point   (x 1 ,  y 1 )   with    slope   m   is  y   m   y   −   y 1     =   m(x −
x 1 ). We find the y-coordinate by plugging x = 2 into the equation y = 2x^3 − 3x^2 − 12x + 20, and
we find the slope by plugging x = 2 into the derivative of the equation.

First,  we  find    the y-coordinate,   y 1     :   y   =   2(2)^3  −   3(2)^2  −   12(2)   +   20  =   0.  This    means   that    the line
passes through the point (2, 0).

Next,   we  take    the derivative:     =   6x^2    −   6x  −   12. Now,    we  can find    the slope,  m:      =

6(2)^2  −   6(2)    −   12  =   0.  Finally,    we  plug    in  the point   (2, 0)  and the slope   m   =   0   to  get the

equation    of  the tangent line:   y   −   0   =   0(x −   2)  or  y   =   0.


  1. y + 29 = −39(x − 5)


Remember    that    the equation    of  a   line    through a   point   (x 1 ,  y 1 )   with    slope   m   is  y   −   y 1     =   m(x −   x 1 ).

We  find    the y-coordinate    by  plugging    x   =   5   into    the equation    y   =    ,  and we  find    the slope

by  plugging    x   =   5   into    the derivative  of  the equation.

First,  we  find    the y-coordinate,   y 1     :   y   =       =   -29.    This    means   that    the line    passes  through

the point   (5, −29).

Next,   we  take    the derivative:     =    .  Now,    we  can find    the
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