Intersection of two planes?

Two distinct planes may be parallel and thus have no intersection at all. If they are not parallel, they intersect in a line.

OK if they are parallel they don't intersect at all, if they are not parallel they intersect as a line. what other option is there?

three planes can intersect as a point or as a line. was the question about three planes? I would not confront your teacher but would recheck the question and if it asks about two planes intersecting I would ask for an explanation, because you don't get it. he might have made a mistake when writing out the test or got it out of a faulty text or you might have misread.

Unless you've left out some key information, I'd say you're right and your teacher is wrong.

Don't be afraid to question your teacher. I was a college instructor for several years, and I encouraged my students to question me if they felt that I was wrong. They did question me frequently which gave us an opportunity to look deeper into the question and get a more thorough explanation. In most cases, I was correct, but I was able to better explain the reasoning because I knew there was a misunderstanding. However, there were times when I was wrong, and I appreciated the students bringing it to my attention. In my mind, as a teacher, the worst thing I could do was to believe that I was infallible and continue teaching incorrect information just to protect my pride. Unfortunately, not all teachers feel that way. Some are offended by students questioning their knowledge. These teachers need to find a new career.

Remember - your teacher may be better educated in his particular area of education, but that doesn't make him more intelligent than you. If you believe you are right, stick to your guns, but be open-minded when your teacher explains the answer.

lines mostly. But mostly the planes come as equations. Look, planes aren't always flat, just coz they are 2d. They could be curved or wavy like a piece of paper that isn't on steady surface. Check the equations for the planes and see if they intersect. It varies frrom plane to plane.

I don't really get the whole plane thing but from what I know they do not go on forever so they can intersect at one point. Just think of it as two squares. You should probly ask your math teacher to explain it for you so that it will make sence.

He's wrong. A one point intersection is the tangent of two intersecting circles. Definitely not a plane.

I don't actually want to post an answer, but this is rather a response to Uz1s's response to Duke's answer (and the comment formatting messed my comment up so...). Duke's method of using a point and a direction vector is correct except for its cross product. The cross product is -i + j - k, which we can find by setting it up as a 3x3 matrix or using Wolfram Alpha.

Two planes cannot be enough to define a single point. It doesn't work when you visualize it, and it doesn't work algebraically. You need three non-parallel planes to define a single point the same way you need three linear equations with three variables (i.e. three equations of the form ax + by + cz = d) to get a unique solution.

for me, as far as my knowledge is concern, your teacher is wrong because two planes always intersect at exactly a line

your teacher is right, since you're talking about 2d planes. they can either intersect or they can be parallel, so the answer is sometimes. if you were talking about 3d planes, your teacher would be wrong.