如图S⊿ADE=﹙1/2﹚XYsinA=12×5/4,∴XY=78 [常数]﹙sinA=5/13﹚
X²Y²=常数.Z²=X²+Y²-2XYcosA=X²+Y²-144
∵X²Y²=常数, ∴当X²=Y²时X²+Y²有最小值,Z²有最小值,Z有最小值,
此时,X²=78
Z²=2×78-144=12Z=2√3.
DE的最小长度=2√3.
如图S⊿ADE=﹙1/2﹚XYsinA=12×5/4,∴XY=78 [常数]﹙sinA=5/13﹚
X²Y²=常数.Z²=X²+Y²-2XYcosA=X²+Y²-144
∵X²Y²=常数, ∴当X²=Y²时X²+Y²有最小值,Z²有最小值,Z有最小值,
此时,X²=78
Z²=2×78-144=12Z=2√3.
DE的最小长度=2√3.