maths question

Chun Hei

2007-03-05 8:13 pm

1.cos30度xcos45度+sin60度xsin45度
2. cos^2 45度xsin30度
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tan^2 60度
3. tan60度 = 開方8xcos45度
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sin(acute angle/3+35度)
4.BCDE is a triangle and ABC is a straight line. If Ad is 20cm,AE =10x開方2and ADE=60度,find the lenght of CD and cx

回答 (1)

用戶19809

2007-03-05 9:10 pm

✔ 最佳答案

(I omitted the degree notation)
sqrt. denotes square root.
(1)
(cos 30)(cos 45)+(sin 60)(sin 45)
=(2 sqrt.)/2[2 cos 30]
=(2 sqrt.)cos 30
=(2 sqrt.)(3 sqrt./2)
=6 sqrt./2
(2)
(cos²45)(sin 30)/tan²60
=(2 sqrt./2)²(1/2)/(3 sqrt.)²
=(1/2)(1/2)/3
=1/12
(3)
tan 60/sin (θ/3+35)=8 sqrt. cos 45
3 sqrt./sin (θ/3+35)=2(2 sqrt.)(2 sqrt.)/2
3 sqrt./sin (θ/3+35)=2
sin (θ/3+35)=3 sqrt./2
Because θ is an acute angle, therefore there is only one solution for θ/3+35
θ/3+35=60
θ/3=25
θ=75
(4)
Is there a figure?
I think it is not showing clearly.

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