The Dot Product - HP 39g Master Manual

The dot product

Eg. 4 Find the angle between the vectors
5
4
3
2
1
-5 -4 -3 -2 -1
-1
-2
-3
-4
-5
On the calculator, the functions DOT and ABS
give the dot product and magnitude
respectively, when fed with vectors. The
hp 39g+ writes vectors as row matrices. For
a =
example
(3, 4)
The calculations are shown in the two screen
shots on the right. Remember to change into
degree mode first.
The list of matrix functions available through the MATH menu is covered
starting on page 271. Not all functions are covered, since many of them go
far beyond the requirements of the average student at whom this book is
aimed.
Using the formula that
(3,4)
θ
(4,1)
where a b
rearrange to obtain:
1 2 3 4 5
Therefore:
would be written as [3,4].
a =
and
(3, 4)
• =
a b a b . .cos
•
is the dot product, we can
cos
θ
cos
θ
175
b =
.
(4,1)
θ
•
a b
θ
=
a b .
•
(3, 4) (4,1)
=
(3, 4) . (4,1)
× + ×
3 4 4 1
=
+ +
2 2 2 2
3 4 . 4 1
16
=
5 17
= ⋅
"
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