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標題: F.3 trigonometric identities 5條 [打印本頁]

作者: billyconan 時間: 10-2-17 05:36 PM 標題: F.3 trigonometric identities 5條

我又唔識做la

~help

圖片附件: Question 1-4.JPG (10-2-17 05:36 PM, 39.97 KB) / 下載次數 46
https://www.2000fun.com/forum.php?mod=attachment&aid=MjY5ODM3fDNlNDJhZjUwfDE3ODY2NTU1NTl8MA%3D%3D

圖片附件: Question 5.JPG (10-2-17 05:36 PM, 24.86 KB) / 下載次數 48
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作者: YSC 時間: 10-2-17 09:50 PM

懶打 x先當成 fita 吧

1/( cos x *sin(90-x))  -  tanx / tan(90-x)

= 1/ cos ^2 (x)  - tan^2 (x) PS: sin(90-x)=cosx  and tan(90-x)= 1/tanx

= (1 - sin^2 x)  /  cos ^2 x PS: tan x = sinx/cosx
= cos^2  x /  cos^2  x
=1

作者: YSC 時間: 10-2-17 09:51 PM

sin 32 = cos (66 - x/2)

cos (90-32) = cos(66- x/2)

58 = 66 - x/2
x/2 = 8
x = 16

作者: YSC 時間: 10-2-17 09:55 PM

tan (x +45) = 1/ tan(x/4)

tan(x+45) = tan (90- x/4)

x+45 = 90- x/4

5x/4 = 45
x = 9 *4 = 36

作者: YSC 時間: 10-2-17 09:57 PM

tan (x + 15) = 1/ tan (x+60)

tan (x+15) = tan(90- x - 60)
x +15 = 30 - x

2x = 15
x = 7.5

作者: YSC 時間: 10-2-17 10:05 PM

1/cos(90-x) - cos(90-x)tan(90-x)/ tanx

=1/ sin x  -  sinx / tan^2 x    PS: 1/tanx =  cosx/ sinx

=1/sinx - sinx * cos^2  x / sin^2 x

= 1/ sinx  - cos^2  x / sinx

= (1- cos^2 x) / sinx

= sin ^2 x / sinx

= sinx

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