Chapter 12 - Section 12.5 - Equations of Lines and Planes - 12.5 Exercises - Page 831: 1

a) True b) False c) True d) False e) False f) True g) False h) True i) True j) False k) True

a) Two lines parallel to a third line are parallel (True) - Their direction vectors are scalar multiplies of the direction of the 3rd line, then they are scalar multiples of each other so they are parallel b) Two lines perpendicular to a third line are parallel (False) - The x-axis and the y-axis are ⊥ to the z-axis but not parallel to each other c) Two planes parallel to a third plane are parallel (True) - Their normal vectors parallel to the normal vector of the 3rd plane, so these two normal vectors are parallel to each other and the planes are parallel d) Two planes perpendicular to a third plane are parallel (False) - The xy plane and yz plane are not parallel to each other but both ⊥ to xz plane e) Two lines parallel to a plane are parallel (False) - The x-axis and y-axis are not parallel to each other but both parallel to the plane z = 1 f) Two lines perpendicular to a plane are parallel (True) - The direction vectors of the lines parallel to the normal vector of the plane, then they parallel to each other , so the lines are parallel g) Two planes parallel to a line are parallel (False) - The planes y = 1 and z = 1 are not parallel but both are parallel to the x-axis h) Two planes perpendicular to a line are parallel (True) - The normal vectors of the 2 planes are parallel to the direction of line, then they are parallel to each other so the planes are parallel i) Two planes either intersect or are parallel (True) j) Two lines either intersect or are parallel (False) - They can be skew k) A plane and a line either intersect or are parallel (True) - They are parallel if the normal vector of the plane and the direction of the line are ⊥ to each other , otherwise the line intersect the plane at the angle 90° - Ф