I took a test today. I wanted to know if I set my limits up correctly and got the right answer, because I've been having problems with that. Okay, here is the question:(adsbygoogle = window.adsbygoogle || []).push({});

A space is bounded by x = 0, y = 0, xy-plane, and the plane: 3x + 2y + z = 6. Find the volume using a double integral.

So, this is how I went about the problem...

Since the space is bounded by the xy-plane, I set z = 0 for the plane. This gave me:

[tex]3x + 2y = 6, y = \frac{-3x+6}{2}[/tex]

That's just an equation of a line, so I plotted that on the xy-plane.

At x = 0, y = 3 (0,3)

At y = 0, x = 2 (2,0)

This is the hard part for me...setting limits. I got:

[tex]0\leq x\leq 2[/tex]

and

[tex]\frac{-3x+6}{2}\leq y\leq 0[/tex]

(hopefully)

*sidenote: If it's wrong, would someone like to show me a simple strategy to setting limits? Also, if there's anything else you could do to help me set limits on integration, that would be really helpful.

To go on with the problem, my resulting double integral was:

[tex]\int_{x=0}^{x=2} \int_{y= \frac{-3x+6}{2}}^{y=0} (-3x-2y+6)dydx[/tex]

integrating with respect to y first, I got:

[tex]\int_{x=0}^{x=2} (-\frac{9}{4} x^2 + 9x-18)dx[/tex]

resulting in answer = 9

Thanks for reviewing.

-Mark

(yay, I learned how to LaTeX :) )

**Physics Forums - The Fusion of Science and Community**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Double Integral Test question

Loading...

Similar Threads for Double Integral Test | Date |
---|---|

A Maximization Problem | Jan 31, 2018 |

I Q about finding area with double/volume with triple integral | Sep 13, 2017 |

I Find total charge (using double integration) | Apr 15, 2017 |

I Integration Limits Changing in Double Integral Order Change | Sep 7, 2016 |

I Change of variables in double integral | Jul 9, 2016 |

**Physics Forums - The Fusion of Science and Community**