幻采圣代
幼苗
共回答了29个问题采纳率:93.1% 举报
您可这样利用公式来
∵在四边形ABCD中,∠ABC=∠ADC=90°
∴在Rt△CAB中,由tan∠CAB = BC/AB=2/3 得:
sin∠CAB = 2/√13
cos∠CAB = 3/√13
另外在Rt△DAE中,由cot∠DAE =AE/DE=2/3 得:
cos∠DAE=2/√13
sin∠DAE=3/√13
∴cos∠DAC = cos(∠DAE -- ∠CAB)
= cos∠DAEcos∠CAB +sin∠DAE sin∠CAB
=(2/√13)( 3/√13)+(3/√13)(2/√13)
= 12/13
即:cos∠DAC = AD / AC = 12/13
而AC=5
∴AD = AC × cos∠DAC
= 5 ×(12/13)
= 60/13
1年前
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