Chapter 2.5 Practice Problems - College of Arts and Sciences

Chapter 2.5 Practice Problems

EXPECTED SKILLS: ? Know the derivatives of the 6 elementary trigonometric functions. ? Be able to use these derivatives in the context of word problems.

PRACTICE PROBLEMS:

1. Fill in the given table:

f (x) sin x cos x tan x cot x sec x csc x

f (x)

d 2. Use the definition of the derivative to show that (cos x) = - sin x

dx Hint: cos ( + ) = cos cos - sin sin

3. Use the quotient rule to show that d (cot x) = - csc2 x. dx

d 4. Use the quotient rule to show that (csc x) = - csc x cot x.

dx

tan 5. Evaluate lim

3

+

h

- tan

3

by interpreting the limit as the derivative of a

h0

h

function at a particular point.

For problems 6-14, differentiate

6. f (x) = 2 cos x + 4 sin x 7. f (x) = 5 cos x + cot x 8. g(x) = 4 csc x + 2 sec x 9. f (x) = sin x cos x

sin2 x 10. f (x) =

cos x 1

11. f (x) = x3 sin x 12. f (x) = sec2 x + tan2 x

x + sec x 13. f (x) =

1 + cos x d2y

For problems 14-17, compute dx2 14. f (x) = tan x 15. f (x) = sin x 16. f (x) = cos2 x 17. f (x) = sin2 x + cos2 x

For problems 18-19, find all values of x in the interval [0, 2] where the graph of the given function has horizontal tangent lines.

18. f (x) = sin x cos x

19. g(x) = csc x

20. 21.

Compute an equation point where x = .

with plots

animate, animate3d, animatecurve, arrow, changecoords, complexplot, complexplot3d,

(1)

of the line which is tangent to the graph of f (x) = conformal, conformal3d, contourplot, contourplot3d, coordplot, coordplot3d, densityplot, display, dualaxisplot, fieldplot, fieldplot3d, gradplot, gradplot3d, implicitplot, implicitplot3d,

inequal, interactive, interactiveparams, intersectplot, listcontplot, listcontplot3d,

listdensityplot, listplot, listplot3d, loglogplot, logplot, matrixplot, multiple, odeplot, pareto,

cos x x

at the

plotcompare, pointplot, pointplot3d, polarplot, polygonplot, polygonplot3d,

polyhedra_supported, polyhedraplot, rootlocus, semilogplot, setcolors, setoptions,

setoptions3d, spacecurve, sparsematrixplot, surfdata, textplot, textplot3d, tubeplot

Consider the graphs of f (x) = 2 cos(x) and g(x) = 2 sin(x) shown below on the a d plot sqrt 2 sin x , x =0.. Pi , scaling =constrained 2

PLOT ...

(2)

interval 0, 2 . b d plot

sqrt

2

cos

x

,

x

=

0 ..

Pi 2

,

scaling

=

constrained

PLOT ...

(3)

display a, b

1.4

1.2

1

0.8

0.6

0.4

0.2

0

3 5 3 7

16

8 16

4 16

8

16

2

x

Show that the graphs of f (x) and g(x) intersect at a right angle when x = . (Hint:

4

Show that the tangent lines to f and g at x = are perpendicular to each other.)

4

2

22. A 15 foot ladder leans against a vertical wall at an angle of with the horizontal, as shown in the figure below. The top of the ladder is h feet above the ground. If the ladder is pushed towards the wall, find the rate at which h changes with respect to at the instant when = 30. Express your answer in feet/degree.

23. Use the Intermediate Value Theorem to show that there is at least one point in the interval (0, 1) where the graph of f (x) = sin x - 1 x3 will have a horizontal tangent 3 line.

24. Multiple Choice: At how many points on the interval [-, ] is the tangent line to the graph of y = 2x + sin x parallel to the secant line which passes through the graph endpoints of the interval? (a) 0 (b) 1 (c) 2 (d) 3 (e) None of these

3

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