F.2 Trigo~

h/tan30+h/tan40=100
h(1/tan30+1/tan40)=100
h(tan60+tan50)=100
h=34.2(3sig.fig)

2007-08-25 19:28:09 補充：
Do not need to use sine law, I think he had not been taught sine law!

2007-08-27 00:19:43 補充：
Let CD be hAD=h/tan40AD=htan50..(1)DB=h/tan30DB=htan60DB=(3^0.5)h..(2)(1)十(2)AD十DB=h(tan50十tan60)AS AD十DB=AB=100100=h(tan50十tan60)

FIRST, angle c is 110 degree
using sin rule (sin law),
100/sin110 = AC/sin30
AC=53.2m

let the point of the line h touch AB be D,
using sin rule again,
as angleCDA is right angle (90degree)
53.2/sin90 = h/sin40
h=34.2m