To find the angle between two vectors in 3D, use the dot product formula: a·b = |a||b|cos(θ). The angle θ can be calculated using the formula θ = arccos( (a·b) / (|a||b|) ). The dot product a·b is computed as a1b1 + a2b2 + a3b3, while the magnitude |a| is found using the square root of the sum of the squares of its components. By substituting the values of the vectors a and b into these equations, the angle can be determined. This method effectively provides the angle between the two specified vectors.