呢題乘數點計牙?????????急!!!!!!聽日交牙!!!

👨🏻‍🏫 學術台數學

wingyan

2008-05-14 3:07 am

呢題乘數點計牙?????????

急!!!!!!
聽日交牙!!!

sin 12 cos 78 + sin 78 cos 12

列曬d steps牙吾該!

thz!

回答 (3)

Wan Chak

2008-05-14 3:24 am

✔ 最佳答案

首先，你要知道以下呢個定理
sin(A+B)
= sinAcosB + cosAsinB

所以
當A = 12，B = 78時
sin12 cos78 + sin78 cos12
= sin (12+78)
= sin90
= 1//

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用戶82723

2008-05-14 3:25 am

cos 78 = cos (90 - 12) = sin 12
sin 78 = sin (90 - 12) = cos 12
Therefore, sin 12 cos 78 + sin 78 cos 12
= sin^2 12 + cos^2 12
= 1

參考: Maths knowledge, without using A. Maths methods

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用戶7639

2008-05-14 3:23 am

sin 12˚ cos 78˚ + sin 78˚ cos 12˚
=sin(12˚+78˚)
=sin90˚
=1

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