Question

AB≥2.8 C为AB中点 CD比B到D长0.5 ∠CDB=60° 求AB+CD最短时 AB CD长

Answer 1

AB+CD最短就要AB=2.8 BC=1.4 设CD为X,则BD为(X+0.5) COS60=(BC^2+CD^2-BD^2)/2BC CD=[1.96+X^2-(X+0.5)^2]/2.8X=1/2 2.8X=3.92+2X^2-2X^2-0.5+2X 0.8X=3.42 X=4.275 所以AB长2.8,CD长4.275