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11.5 Lines and Planes in Space For an animation of this topic visit:

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**The parametric equations of a line**

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**Symmetric equations of the line**

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Example 1 Find the parametric and symmetric equations of the line L that passes through (1,-2,4) and is parallel to v = <2,4,-4>

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Example 1 solution Find parametric and symmetric equations of line L that passes through the point (1,-2,4 ) and is parallel to v = <2,4,-4> Solution to find a set of parametric equations of the line, use the coordinates x1 =1, y1=-2, z1 = 4 and direction numbers a=2, b = 4 and c=-4 x= 1+2t, y = -2+4t, z=4-4t (parametric equations) Because a,b and c are all nonzero, a set of symmetric equations is

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Example 2 Find a set of parametric equations of the line that passes through the points (-2,1,0) and (1,3,5), Graph the equation (next slide shows axis).

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Example 2 solution

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**Problem 26 Determine if any of the following lines are parallel.**

L1: (x-8)/4 = (y-5)/-2 = (z+9)/3 L2: (x+7)/2 = (y-4)/1 = (z+6)/5 L3: (x+4)/-8 = (y-1)/4 = (z+18)/-6 L4: (x-2)/-2 = (y+3)/1 = (z-4)/1.5

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Problem 28 Determine whether lines intersect, and if so find the point of intersection and the angle of intersection. x = -3t+1, y = 4t + 1, z = 2t+4 x=3s +1, y = 4s +1, z = -s +1

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**Solution 28 x = -3t+1, y = 4t + 1, z = 2t+4**

x=3s +1, y = 4s +1, z = -s +1 Set x y and z equations equal -3t+1 =3s s +1 = 4t s +1 = 2t+4 From the first one we get s=-t When s=-t is plugged into the second we get t=1/3 When plugged into the third equation we get t = -3 Hence the lines do not intersect

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Problem 30 Determine whether lines intersect, and if so find the point of intersection and the angle of intersection. (x-2)/-3 = (y-2)/6 = z-3 (x-3)/2=y+5=(z+2)/4

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**Hint on Problem 30 (x-2)/-3 = (y-2)/6 = z-3 (x-3)/2=y+5=(z+2)/4**

Write the equations in parametric form Then solve as per #28 These do intersect. Use the dot product of the direction vectors to find the angle between the two lines <-3,6,1> ∙ <2,1,4>

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Example 3 Find the equation of a plane containing points (2,1,1), (0,4,1) and (-2,1,4)

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Example 3 Solution

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Drawing a plane

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Chapter 2 Section 2.4 Lines and Planes in Space. x y z.

Chapter 2 Section 2.4 Lines and Planes in Space. x y z.

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