In mathematics, two unknowns can be found from three known numbers.

For example, in triangle ABC, it is known that angle C=90 degrees, angle A=30 degrees, AB= 10,

Question: AC and BC

Solution: Because in triangle ABC, angle C=90 degrees, angle A=30 degrees, AB= 10,

So BC=AB/2= 10/2=5.

From Pythagorean Theorem: AC= radical sign (AB 2-BC 2)

= root sign (10 2-5 2)

= root number 75

The root number 3 of =5.