If two parallel planes are cut by a third plane, then the lines of intersection are

Parallel planes are two planes that do not intersect.

Theorem:  If two parallel planes are cut by a third plane, then the lines of intersection are parallel.

In the attached picture you can see two parallel planes P and M that are cut by plane R. The lines of intersection are:

Conclusion: AB||CD.

parallel.

hello from mrbilldoesmath!

answer:

a(n) - a(n-1) -3

discussion:

this ones a bit interesting. given a(n) = 5 - 3n consider this:

a(n-1) = 5 - 3(n-1)

          = (5 - 3n) + 3             => but a(n) = 5 - 3n, the first term

          = a(n)   + 3                 => subtract 3 from both sides

a(n-1) -3 = a(n)  

or

a(n) - a(n-1) -3

you,

mrb

a

step-by-step explanation:

a