In triangle ABC, it is known that angle C = 90 °, angle A = 30 °, CD – height, BD = 7 cm. Find the hypotenuse AB.

If the first angle is 90 and the second is 30, then the third is 60.
Therefore, in the small triangle formed inside the large (CDB), the smaller of the angles is 30 degrees, and opposite it lies the leg, which is 50% of the hypotenuse.
Thus, in the triangle CDB, the leg DB is 7 cm, and the hypotenuse CB = 14 cm.
In turn, CB is a leg opposite an angle of 30 degrees of triangle ABC, which means hypotenuse AB = 28 cm.