Question

(1 point) Find ⋅ if =⟨−1,0,1⟩ and =⟨4,5,2⟩ Is the angle between the vectors "acute", "obtuse" or "right"?

Answer 1

Obtuse.

Explanation:

If we have a vector v = (a, b, c)

The magnitude of the vector is:

|v| = √(a^2 + b^2 + c^2)

And the dot product of two vectors:

v = (a, b, c)

w = (c, d, e)

is:

v.w = |v|*|w|*cos(θ) = a*c + b*d + c*e

With that relation, we can find the angle between the two vectors.

In this case, we have:

v = ⟨−1,0,1⟩

then:

|v| = √( (-1)^2 + 0^2 + 1^2) = √2

And:

w = ⟨4,5,2⟩

then:

|w| = √( 4^2 + 5^2 +2^2) = √116

Then:

v.w = (√2)*(√116)*cos(θ) = (-1)*(4) + 0*5 + 1*2

(√2)*(√116)*cos(θ) = -4 + 2 = -2

(15.23)*cos(θ) = -2

cos(θ) = -2/15.23

θ = Acos( -2/15.23) = 97.5°

Then the angle is larger than 90°, so the angle is obtuse.