Hello, I just joined this Physics Forum, and here is my problem:(adsbygoogle = window.adsbygoogle || []).push({});

1. The problem statement, all variables and given/known data

Find an equation for the surface obtained by rotating the line y=3x+2 about the x-axis.

2. Relevant equations

y=3x+2 is the given line

equation for flat side of cone or a circle:

z^2=x^2+y^2 => r^2=x^2+y^2

3. The attempt at a solution

If you rotate this line y=3x+2 about the x-axis on a 3D coordinate system you get a cone, 2 cones pointed at each other.

Is the "equation for the surface" meaning the circular part of the cone?

If so, is the equation then

|3x+2|^2

r^2=x^2+y^2

the r^2 in r^2=x^2+y^2 is the |3x+2|^2

so, |3x+2|^2=y^2+z^2

=9x2+12x+4 =y^2+z^2 ??is this the equation??

Any help would be appreciated

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# Homework Help: Find an equation for the surface by rotating

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