SHARING.... -experiences of teaching maths as a hobby for over 50 years to school and college students. -challenges in project management and the common sense approach to it from old classics.

Friday, February 27, 2015

COORDINATE GEOMETRY
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Please help solve the following and show all work please. Thank you!
1.) Find the center and radius of the sphere x^2+y^2+z^2-2x+4z-4=0
2.) Find the projection of PQ onto PR given the points P(-1,2,4), Q(3,0,-2), and R(-5,-3,6)
3.) Find the initial point of vector u=<3,-2,11>, if the terminal point is B(-6,2,-1)
4.) Find the work done as a force F=<-4,2,8> moves an object from point P(9,-1,-3) to Q(2,4,-5).
5.) Write the equation of the plane containing the points P(-5,5,0), Q(3,3,0), and R(-4,-1,-5)
1…..
[X-1]^2+Y^2+[Z+2]^2=4+1+4=9
HENCE CENTER OF SPHERE IS [ 1 , 0 , - 2 ]
AND RADIUS = 3 UNITS
2…………….
P-124
Q30-2
R-5-36
PQ=Q-P=4-2-6
PR=R-P=-4-52
PROJECTION OF PQ ON TO PR = [{PQ.PR}/|PR|]*PR
PQ.PR= -16+10-12=-18
|PR|=[16+25+4]^0.5 = 45^0.5=6.708204
PROJECTION OF PQ ON TO PR =-2.68328*[ - 4 , - 5 , 2 ]
3……
U=3-211
B=-62-1
I=B-U=-94-12
INITIAL POINT IS [ - 9 , 4 , - 12 ]
4…..
F=-428
P=9-1-3
Q=24-5
PQ=Q-P=-75-2
WORK DONE = F.[PQ]=28+10-16=22
5…..
P=-550
Q=330
R=-4-1-5
EQN. OF PLANE THROUGH Q IS
A[X-3]+B[Y-3]+CZ = 0 ………………………………….1
PUTTING P & R IN THIS …
-8A+2B=0…………………B=4A
-7A-4B-5C=0……5C=-23A…..C=-4.6A
HENCE EQN. OF PLANE IS …
[X-3]+4[Y-3]-4.6Z=0
X+4Y-4.6Z=15
5X+20Y-23Z=75………….ANSWER

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