# Vector problem

brad sue
Hi please, someone help me with those problems?

It's about three dimension space and it is about vectors properties:

Find the unit vectors u that are prependicular to both i+2j+k and 3i-4j+2k.

the second is:

Find two mutually perpendicular unit vectors that are perpendicular to 2i+3j

Thank you for your help

Brad

## Answers and Replies

da_willem
Express the vector(s) you seek in terms of unknown coefficients (e.g. ai+bj+ck) and use the definition of 'perpendicular' (i.e. the dotproduct is zero) to find equations you can solve for these unknowns.

Homework Helper
You can also use the fact that the outer product (vectorial) of two vectors gives a new vector which is perpendicular to the first two. Divide by the norm to make it a unit vector.

brad sue
thanks

OK I going to try your suggestion

da_willem said:
Express the vector(s) you seek in terms of unknown coefficients (e.g. ai+bj+ck) and use the definition of 'perpendicular' (i.e. the dotproduct is zero) to find equations you can solve for these unknowns.

mathmike
a vector perpendicular to two separate vectors is created by using the cross product