What is the dot product of <5,1,-7> and <8,4,9>?

2 Answers

The dot product of two three dimensional vectors is defined as

a*b=a_x*b_x+a_y*b_y+a_z*b_z

In our case a=(5,1,-7) and b=(8,4,9)

hence

a*b=5*8+1*4-7*9=-19

Jan 3, 2016

-19

Explanation:

To do the dot product, you multiply together the corresponding components, and then sum the results. In general:
(a_1, a_2, a_3)*(b_1, b_2, b_3)=(a_1b_1+a_2b_2+a_3b_3)

So in your case:

(5*8)+(1*4)+(-7*9)
=40+4-63
=-19