Then 0≤X≤ 10 (that is, 0≤AP≤AB).
(2) If the angle CPN = 60 and CN=PN, then △CPN is an equilateral triangle, then CP=6 decimeters, and X=AP= 12-CP=6 decimeters.
(3) The shadow area of an umbrella under direct sunlight is actually the area of a circle with EF as its diameter. Connect EF and CA at point d, right triangle CFD, according to pythagorean theorem: DF? =CF? -CD? And CD = ca-x =12-X.
Shadow area under umbrella Y=π×DF? =π×(CF? -CD? )=π×{ 18? -( 12-X)? }=
Work out the result, do the calculation, and it's done. )