CODEWITHSUNDEEP
math
OliveOne
OliveOne

Reputation: 338

How to calculate obtuse angle between two vectors?

How to calculate obtuse angle between two vectors if both vectors and x axis is given. First vector can be taken as x axis. we can get acute by dot product and acos.

Upvotes: 4

Views: 15253

Answers (2)

Paul
Paul

Reputation: 1

It is necessary to use both dot and cross products to correctly resolve the angle. Angle between vectors u and v is 

||atan2(s,c)||
where `s = ||u X v||`  (magnitude of the cross product)
and `c = u.v`        (dot product)

and atan2 is the 4-quadrant inverse tan function

and ||*|| denotes magnitude (norm).

This will always return an angle between 0 and 180 degrees.

Upvotes: 0

KJ Saxena
KJ Saxena

Reputation: 21848

Before applying acos, check if the dot product is negative. If negative, the angle is obtuse :)

Further, as acos has a range of 0 to pi, you will do fine as long as you do not want reflex angles (>pi)

Upvotes: 5

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