Calculus Question: Vectors?

Question

If anyone could help explain to me how to approach this problem, it'd be great. Thanks.

find a x b

a=2i+3j

b=i-3j

-the answer is -7

Points awarded!

Answer 1

I assume this is a dot product.

you have...

<2,3> dot <1,-3> = (2)(1) + (3)(-3) = -7

<a,b> dot <c,d> = ac + bd

Answer 2

A word of warning: We typically write a x b to mean the cross product.  Since the cross product a x b = -9k, I assume you actually want the dot product (also called the "inner product").

I haven't found a particularly good way to write the dot product with ascii, but I usually use the asterisk *.

a * b = (2 * 1) + (3 *-3) = 2 + -9 = -7.