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**1. Homework Statement**

Ok, given 3 planes pi1, pi2 and pi3 with vector equations

**r**.

**n1**=0,

**r**.

**n2**=0 and (

**r**-

**a**).

**n3**=0 respectively, where

**a**,

**n1**,

**n2**,

**n3**are given vectors. No 2 planes are parallel and the third plane is parallel to the line, L, given by the intersection of planes pi1 and pi2. Consider the triangle obtained by intersection of all three planes by a plane perpendicular to L. Find a formula for the area and express it only in terms of the scalars:

**a**.

**n3**, |

**n1**x

**n2**|, |

**n1**x

**n3**| and |

**n2**x

**n3**|.

**2. Homework Equations**

See above

**3. The Attempt at a Solution**

Too many failed attempts... But I guess start of with or end up with some sort of equation that looks like A=0.5|

**u**x

**v**| (i.e. area of a triangle using vectors).

I also believe planes pi1 and pi2 have a common point at (0,0,0). I dunno how to find other common points without turning things into lots of variables via cartesian equations.

I've beens stuck on this question for about 12 hours (not consecutively of coures) and still can't figure out the answer... Any help will be appreciated!

Thanks in advance,

- TOD