Solução_Calculo_Stewart_6e

F.
TX.10
CHAPTER 13 REVIEW ET CHAPTER 12 ¤ 133
19. Here the vectors a = h4 − 3, 0 − (−1) , 2 − 1i = h1, 1, 1i and b = h6 − 3, 3 − (−1), 1 − 1i = h3, 4, 0i lie in the plane,
so n = a × b = h−4, 3, 1i is a normal vector to the plane and an equation of the plane is
−4(x − 3) + 3(y − (−1)) + 1(z − 1) = 0 or −4x +3y + z = −14.
21. Substitution of the parametric equations into the equation of the plane gives 2x − y + z =2(2− t) − (1 + 3t)+4t =2 ⇒
−t +3=2 ⇒ t =1.Whent =1, the parametric equations give x =2− 1=1, y =1+3=4and z =4. Therefore,
the point of intersection is (1, 4, 4).
23. Since the direction vectors h2, 3, 4i and h6, −1, 2i aren’t parallel, neither are the lines. For the lines to intersect, the three
equations 1+2t = −1+6s, 2+3t =3− s, 3+4t = −5+2s must be satisfied simultaneously. Solving the first two
equations gives t = 1 , s = 2 and checking we see these values don’t satisfy the third equation. Thus the lines aren’t parallel
5 5
andtheydon’tintersect,sotheymustbeskew.
25. n 1 = h1, 0, −1i and n 2 = h0, 1, 2i. Settingz =0, it is easy to see that (1, 3, 0) is a point on the line of intersection of
x − z =1and y +2z =3. The direction of this line is v 1 = n 1 × n 2 = h1, −2, 1i. A second vector parallel to the desired
plane is v 2 = h1, 1, −2i, since it is perpendicular to x + y − 2z =1. Therefore, the normal of the plane in question is
n = v 1 × v 2 = h4 − 1, 1+2, 1+2i =3h1, 1, 1i. Taking(x 0 ,y 0 ,z 0 )=(1, 3, 0), the equation we are looking for is
(x − 1) + (y − 3) + z =0 ⇔ x + y + z =4.
27. By Exercise 13.5.73 [ ET 12.5.73], D =
|2 − 24|
√
26
= 22 √
26
.
29. The equation x = z represents a plane perpendicular to
the xz-plane and intersecting the xz-plane in the line
x = z, y =0.
31. The equation x 2 = y 2 +4z 2 represents a (right elliptical)
cone with vertex at the origin and axis the x-axis.
33. An equivalent equation is −x 2 + y2
4 − z2 =1,a
hyperboloid of two sheets with axis the y-axis. For
|y| > 2, traces parallel to the xz-plane are circles.
35. Completing the square in y gives
4x 2 +4(y − 1) 2 + z 2 =4or x 2 +(y − 1) 2 + z2
4 =1,
an ellipsoid centered at (0, 1, 0).