In triangle ABC, angle C = 60 degrees, angle B = 90, height BB1 = 2cm. What is the AB side?

This is a right-angled triangle, because it has one angle equal to 90 degrees, so the angle is A = 180-90-60 = 30 degrees.
Since in a rectangular triangle the side lying opposite an angle of 30 degrees = 1/2 of the hypotenuse, the side we know means the hypotenuse AB = 2 * 2 = 4

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