幾難，我計五到!!

14)
tan∠ACB=AB/BC}
∠ACB=32˚}
=>tan32˚=AB/BC
=>AB=tan32˚BC}
AB+BC=28cm/2=14cm}
=>tan32˚BC+BC=14cm
=>BC≈8.616cm
=>AB≈5.384cm

=>AB=CD=5.384cm,AD=BC=8.616cm

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15)
(a)MN⊥BD=>∠BNM=90˚}
CD⊥BC=>∠BCD=90˚}
MB=MB}
NB=BC}
=>△BCM全等於△BNM

(b)
S△BCD=(5*5)/2=12.5cm^2}
S△BCD=S△DMB+S△BCM}
S△DMB=(CM*BD)/2=(CM*5√2)/2}
S△BCM=(CM*BC)/2=(5CM)/2}
=>12.5=(CM*5√2)/2+(5CM)/2
=>CM=25/(5√2+5)≈2.071(cm)

2007-02-27 20:43:25 補充：
樓上看錯了,∠ACB是32˚不是28˚ar!

14.LET AB BE x , AD be y
2x+2y = 28
x+y=14
y=14-x
x / (14-x ) = tan 28
x = 0.531709431 * (14 -x )
x = 7.443932043 - 0.531709431x
1.531709431x = 7.443932043
x = 4.859885232
y = 14 - 4.8598853232
y = 9.140114768
therefore x = 7.44 y= 9.14 (corr.to 3 sign. fig.)
15. 睇唔清楚個圖..

2007-02-28 01:00:24 補充：
.LET AB BE x , AD be y2x+2y = 28x+y=14y=14-xx / (14-x ) = tan 32x = 0.624869351 * (14 -x )x = 8.748170927 - 0.624869351x1.624869351x= 8.748170927x = 5.383922665y = 14 - 4.8598853232y = 8.616077335therefore x = 5.38 y= 8.62 (corr.to 3 sign. fig.)15. 睇唔清楚個圖..