5128_Ch03_pp098-184

162 Chapter 3 Derivatives
2. y 1 2 9 , x2 y
3 2 2 9 x2
3
EXAMPLE 6 Using the Rational Power Rule
d d
(a) x x d x d x
12 1 1
2 x12
2 x
Notice that x is defined at x 0, but 12x is not.
d
(b) x d x
23 2 3 2
x13
3x
13
The original function is defined for all real numbers, but the derivative is undefined at
x 0. Recall Figure 3.12, which showed that this function’s graph has a cusp at x 0.
d
(c) cos x d x
15 1 5 cos d
x65 • cos x d x
1 5 cos x65 sin x
5. y 1 2x 3, x 2 y 2 2x 3 x 2
Quick Review 3.7 (For help, go to Section 1.2 and Appendix A.5.)
1 5 sin xcos x65 Now try Exercise 33.
xy2
8. y x 2
y x
In Exercises 1–5, sketch the curve defined by the equation and find
two functions y 1 and y 2 whose graphs will combine to give the curve.
1. x y 2 0 y 1 x, y 2 x 2. 4x 2 9y 2 36
3. x 2 4y 2 x x
0 y 1 , y2 4. x 2 y 2 9
2 2
5. x 2 y 2 2x 3
y 1 9 , x 2 y 2 9 x 2
In Exercises 6–8, solve for y in terms of y and x.
6. x 2 y2xy 4x y y 4x y 2xy
x 2
Section 3.7 Exercises
In Exercises 1–8, find dydx.
4. y x (x y)2 or 1 3x
2xy
x2
1
1. x 2 y xy 2 6 2 xy
y2
2. x 3 y 3 18xy 6 y x2
2xy
x2
y 2
6x
3. y 2 x 1 1
4. x
x 1
x
y
y(x 1) 2
x y
5. x tan y cos 2 y 6. x sin y sec y
1 y
7. x tan xy 0 See page 164. 8. x sin y xy
x cos y
In Exercises 9–12, find dydx and find the slope of the curve at the
indicated point.
dy x
,23
9. x 2 y 2 dx y
13, (2, 3)
dy x
10. x 2 y 2 9, (0, 3)
,0
dx y
dy x 1
11. (x 1) 2 (y 1) 2 13, (3, 4) , 23
dx y 1
12. (x 2) 2 (y 3) 2 25, (1, 7) See page 164.
In Exercises 13–16, find where the slope of the curve is defined.
13. x 2 y xy 2 4 See page 164. 14. x cos y See page 164.
15. x 3 y 3 xy See page 164. 16. x 2 4xy 4y 2 3x 6
See page 164.
In Exercises 17–26, find the lines that are (a) tangent and
(b) normal to the curve at the given point.
17. x 2 xy y 2 1, 2, 3 (a) y 7 4 x 1 2 (b) y 4 7 x 2 9
7
18. x 2 y 2 25, 3, 4 (a) y 3 4 x 2 5
4
19. x 2 y 2 9, 1, 3
(b) y 4 3 x
See page 164.
7. ysin x x cos x xyy
8. xy 2 y yx 2 y
y y x cos
x
sin
x x
In Exercises 9 and 10, find an expression for the function using
rational powers rather than radicals.
9. xx 3 x x 32 x 56 10. x 3
x
2 x
x
3
12 x 56
x
25. (a) y 2x 2 (b) y 2 1
2
20. y 2 2x 4y 1 0, 2, 1 (a) y x 1 (b) y x 3
21. 6x 2 3xy 2y 2 17y 6 0, 1, 0 See page 164.
22. x 2 3xy 2y 2 5, 3, 2 (a) y = 2 (b) y 3
23. 2xy p sin y 2p, 1, p2 See page 164.
24. x sin 2y y cos 2x, p4, p2 (a) y 2x (b) y 1 2 x 5
8
25. y 2 sin px y, 1, 0
26. x 2 cos 2 y sin y 0, 0, p (a) y (b) x 0
In Exercises 27–30, use implicit differentiation to find dydx and then
d 2 ydx 2 .
27. x 2 y 2 1 See page 164. 28. x 23 y 23 1 See page 164.
29. y 2 x 2 2x See page 164. 30. y 2 2y 2x 1
See page 164.
In Exercises 31–42, find dydx.
31. y x 94 (9/4)x 5/4 32. y x 35 (3/5)x 8/5
33. y 3 x (1/3)x 2/3 34. y 4 x (1/4)x 3/4
35. y 2x 5 12 (2x 5) 32 36. y 1 6x 23 4(1 – 6x) 1/3
37. y xx 2 x
1 38. y (x 2 1) 3/2
x 2 (x 2 1) 1/2 (x 2 1) 1/2
x
2
1
39. y 1 x See page 164. 40. y 32x 12 1 13
See page 164.
41. y 3csc x 32 See page 164. 42. y sin x 5 54
See page 164.