Question from kyrie, a student:

Find the possible values of the constant a such that | ai + 4aj + 4k | = 13 I know the answer is 3 but not sure how to get to it

Kyrie,

The length of a vector pi + qj + rk is designated |pi + qj + rk| and is given by the expression

|pi + qj + rk| = √(p^{2} + q^{2} + r^{2}).

For your vector this means that

√(a^{2} + (4a)^{2} + 4^{2}) = 13

Solve for a.

Penny