用三角函数计算!如图所示,角DAC等于30°,AB等于10,角DBC等于45°,已知AE等于1.44,求DF的长(计算精

ABD-135° ,ADB=15°
AB/sin15°=AD/sin135° ,AD=10sin135°/sin15°=27.2m
DF=1.44+DC=1.44+27.2/2=15.m
解法二：
角DBC等于45°,则BC=DC ,AC=10+DC ,AD=2DC
AD^2=(10+DC)^2+DC^2=4DC^2
100+20DC+DC^2+DC^2=4DC^2
DC^2-10DC-50=0
DC=[10±√(300)]/2=5+5x1.732=13.66
DF=1.44+DC=1.44+13.66=15m