Dot product to find the angle between two vectors

[icelated]

I am trying to use the Dot product to find the angle between two vectors
P = 3i + 4j
q = i - 2j

would i use this formula?

theta = cos-1( p times q) / pq

if so, this is wht i have so far

vector p times q = (3)(1) + (4)(-2) = -5

vector p = square root 3^2 + 4^2 = 5
vector q = square root 1^2 +(-2)^2 = square root 5

then plug it into the original equation

cos^-1( -5 /5square root 5) = 116.565 degrees

does that seem right or am i completely wrong?

 

[Deleted member 4993]

I am trying to use the Dot product to find the angle between two vectors
P = 3i + 4j
q = i - 2j

would i use this formula?

theta = cos-1( p times q) / pq

if so, this is wht i have so far

vector p times q = (3)(1) + (4)(-2) = -5

vector p = square root 3^2 + 4^2 = 5
vector q = square root 1^2 +(-2)^2 = square root 5

then plug it into the original equation

cos^-1( -5 /5square root 5) = 116.565 degrees

does that seem right or am i completely wrong?

You are correct.