Number Ruby

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  4. This matrix rotates counterclockwise around the origin
require "matrix"
unit = 2
theta = Math::PI/2     # 90 degrees
rotate = Matrix[[Math.cos(theta), -Math.sin(theta)],
                [Math.sin(theta),  Math.cos(theta)]]
rotate*unit            # [-1.0, 1.0]: 90 degree rotation