1 trigonometry Q.

你好，我是STY，我的解答如下：

4sinxcosx = 1

As sin2x = 2sinxcosx,

4sinxcosx = 2sin2x

2sin2x = 1

sin2x = 1/2

2x = 30, 150, 390, 510

x = 15, 75, 195, 255


希望可以幫到你，唔明可以再問我

By STY~

2011-08-05 23:32:06 補充：
Let me perform a wasy question to you

Let x = 3,

Squaring both sides,

x^2 = 9

x = 3 or -3

-3 is the wrong root, right?

but...well, some root don't appear?do you have any example?

just ask here...

2011-08-05 23:32:12 補充：
how to prevent?

you must learn 驗算in primary...

just do the same thing

http://hk.knowledge.yahoo.com/question/question?qid=7011080500807

this is my previous answer...

this question has to do the 驗算...

the important thing is you must do 驗算

after you get the answer of squaring both sides