F.4 Amaths>>>>trigo~~

Sheep~

我想問下面呢兩條數點做???
我做極都做唔到...

同埋做D PROVE的TRIGO有冇D咩方法?
有冇D咩技巧會做快D?

THX![[onion_20]][[onion_20]]
Q1係prove,Q2係SOLVE

[ 本帖最後由 Sheep~ 於 16-6-2008 23:40 編輯 ]

[S]【YU】

1. 煩字  C = 180 - (A+B)
2. product to sum 應該唔難.

Sheep~

我試過product to sum <<<
平時轉完應該有舊野約左..
但係做到呢步就做唔到..
之後就唔識解~

piyopiyo

原帖由 Sheep~ 於 15-6-2008 18:57 發表
我試過product to sum  

應該係計錯左d野
我n年前都做過第2題...我記得都係用 p to s去搞...第1題係煩到hihi

Zend

2)
sin6xsinx =2sin3xcos3xsinx
sin6xsinx=cos3xcos4x
sin6xsinx-cos3xcos4x=0
2sin3xcos3xsinx-cos3xcos4x=0
cos3x(2sin3xsinx-cos4x)=0
cos3x (2(-1/2)(cos4x-cos2x)-cos4x)=0
cos3x(cos2x-2cos4x)=0
cos3x = 0 or cos2x=2cos4x
cos4x =2cos^2 2x -1
solve it

sinA/2+sinB/2+sinC/2 =1+sin(45'-A/4)sin(45'-B/4)sin(45'-C/4)
let A= 30'
B = 60'
C=90'
A/2 =15'
B/2 =30'
C/2 = 45'
A/4 =7.5'
B/4=15'
C/4 = 22.5'

sinA/2+sinB/2+sinC/2 = sin15'+sin30'+sin45'=1.4659
1+sin37.5sin30sin22.5=1.1164 =.="?

[ 本帖最後由 Zend 於 16-6-2008 01:44 編輯 ]

piyopiyo

原帖由 Zend 於 16-6-2008 01:13 發表
2)
sin6xsinx =2sin3xcos3xsinx
sin6xsinx=cos3xcos4x
sin6xsinx-cos3xcos4x=0
2sin3xcos3xsinx-cos3xcos4x=0
cos3x(2sin3xsinx-cos4x)=0
cos3x (2(-1/2)(cos4x-cos2x)-cos4x)=0
cos3x(cos2x-2cos4x)=0
cos3 ...

I wonder if 樓主 wants us to simplify or prove Q.2[[onion_44]]

Zend

sin6xsinx=cos3xcos4x

let x =10' (if we need to prove ge wa)
sin60sin10=0.1503
cos3xcos4x = cos30cos40=0.6634

Sheep~

佢呢係就係叫你搵個x,可以就咁sub數入去咩??

x^2+x=5
sub x=10,
l.h.s=110
r.h.s.=5
所以條數有問題??

Zend

原帖由 piyopiyo 於 16-6-2008 08:30 AM 發表

I wonder if 樓主 wants us to simplify or prove Q.2[[onion_44]]

所以我用contradiction 證明唔係simplify lor =.=....

[S]【YU】

通常simplify 都唔會係equation-.- 唔駛證掛...