Solution: In Rt△BCD, ∠ B = 90, ∠ BDC = 40, and DB=5m.
∫tan∠BDC =
BC/DB
Substitution data: BC = 5× tan 40 ≈ 4. 195.
∴EB=BC+CE=4. 195+2≈6.20m
EB is 6.20 meters high.
2
DE⊥BC, AF⊥BC and vertical foot are E and F respectively.
< ADC = 135, then < c = 45,
DE=DCsin45 =8*√2/2=4√2,
CE=DE=4√2
FE=AD=6,
BF=BC-CE-EF=30-6-4√2=24-4√2
AF=DE=4√2
tanB = AF/BF = 4√2/(24-4√2)=(3√2+ 1)/ 17≈0.30835,
〈B≈ 17. 13,
2、v=( 1/2)(6+30)*(4√2)* 100=7200√2≈ 10 180.8(m^3)
,
The construction of this dam requires earthwork 10 180.3 cubic meters.