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A sphere with radius 7 has its center at the origin of the 3D cartesian grid shown on the left. Consider only the top half of the sphere:

Calculate the value of z, the slope in the x-direction and the slope in the y-direction at the two points where (x,y) are (2.3,-0.8) and (-0.5,1.4).

 

z (2.3, -0.8)= correct answer is 6.56

x ('''''''''''''')= correct answer is -0.35

y ('''''''''''''')= correct answer is 0.12

z(-0.5, 1.4)= correct answer is 6.84

x ('''''''''''''')= correct answer is 0.07

y ('''''''''''''')=correct answer is -0.20.

 

Thanks guys. This is the full question.

 Sep 5, 2014

Best Answer 

 #1
avatar+33616 
+5

The general equation for a sphere, centred at (0,0,0) is  x2 + y2 + z2 = r2

Rearrange this as  z = (r2 - x2 - y2)1/2    

The slope of z with respect to x is given by

∂z/∂x = -x/ (r2 - x2 - y2)1/2

The slope of z with respect to y is given by

∂z/∂y = -y/ (r2 - x2 - y2)1/2

 

You have the values of x, y and r, so I'll leave you to plug them into these formulae.

 Sep 5, 2014
 #1
avatar+33616 
+5
Best Answer

The general equation for a sphere, centred at (0,0,0) is  x2 + y2 + z2 = r2

Rearrange this as  z = (r2 - x2 - y2)1/2    

The slope of z with respect to x is given by

∂z/∂x = -x/ (r2 - x2 - y2)1/2

The slope of z with respect to y is given by

∂z/∂y = -y/ (r2 - x2 - y2)1/2

 

You have the values of x, y and r, so I'll leave you to plug them into these formulae.

Alan Sep 5, 2014

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