Please find the follows...
1) sin(A+B)
2) cos(2A)
3) sin(A/2)
Thank you~
更新1:
The List of Equations: http://img373.imageshack.us/img373/7171/20080522003bn0.jpg
Problem about Trig.
2008-05-23 9:54 pm
Given sinA = (3/5), A in quadrant II, and cosB = (7/25), B in quadrant I.
Please find the follows...
1) sin(A+B)
2) cos(2A)
3) sin(A/2)
Thank you~
Please find the follows...
1) sin(A+B)
2) cos(2A)
3) sin(A/2)
Thank you~
回答 (1)
2008-05-23 10:09 pm
✔ 最佳答案
1. sin(A+B) =sinAcosB+cosAsinBcosA=-4/5
sinB=24/25
so sin(A+B) =(3/5)(7/25)+(-4/5)(24/25)
=-3/5
2.cos(2A)=1-2sin^2 A
=1-2*(3/5)^2
=7/25
3.cos(2A)=1-2sin^2 A
so cos(A)=1-2sin^2 (A/2)
-4/5 = 1- 2sin^2 (A/2)
2sin^2 (A/2)=1+4/5
sin^2 (A/2)=0.9
sin(A/2)=3/ (sq rt 10) or -3/ (sq rt 10) (reject)
-3/ (sq rt 10) reject since when we finding A/2, it is in quadrant I
參考: my math knowledge
收錄日期: 2021-04-29 21:45:46
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20080523000051KK00919