Why Is My Calculation of the Scalar Product Incorrect?

[elpermic]

Homework Statement

Find the scalar product of the 2 vectors.
Vector A is north of east at 70 degrees with a magnitude of 3.60m
Vector B is south of west at 30 degrees with a magnitude of 2.40m

Homework Equations

ABcosx

The Attempt at a Solution

I did dot product using the formula, 3.60x2.40xcos(-100) and got the wrong answer.. The answer is 13.00. What the hell did I do wrong? I did as the formula said I should do and failed. I don't get it??

 

[tiny-tim]

Vector A is north of east at 70 degrees …
Vector B is south of west at 30 degrees …

I did dot product using the formula, 3.60x2.40xcos(-100) …

Hi elpermic!

It ain't 100. ​

 

[Doc Al]

I did dot product using the formula, 3.60x2.40xcos(-100) and got the wrong answer.. The answer is 13.00.

(1) The formula calls for the angle between the two vectors. That angle is not 100°. (Draw a diagram.)
(2) The answer cannot be 13.