an equation

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Valentas

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Dec 19, 2010
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Well guys I haven't been at school when teacher was explaining quations like this:

(cos5x - 5)(5sin5x - 2.5)=0

I may use the rule: one multiplicative must be zero

E.G. cos5x - 5=0 and 5sin5x - 2.5=0

I think I should get 2 solutions but in the answers there is only one. If you don't know what I'm talking about, please solve this on your method :)

another equation: ctgx(2 - cosx)=0

I get the idea that cosx=0 -----> x= pi/2 + npi

but what to do with 2 - cosx ? again only one answer above x= :)
 
Valentas said:
Well guys I haven't been at school when teacher was explaining quations like this:

(cos5x - 5)(5sin5x - 2.5)=0

I may use the rule: one multiplicative must be zero

E.G. cos5x - 5=0 and 5sin5x - 2.5=0

I think I should get 2 solutions but in the answers there is only one. If you don't know what I'm talking about, please solve this on your method :)

another equation: ctgx(2 - cosx)=0

I get the idea that cosx=0 -----> x= pi/2 + npi

but what to do with 2 - cosx ? again only one answer above x= :)
Click to expand...

You have to remember:

|cos(?)| ? 1

and

|sin(?)|? 1

That is the magnitudes of the sine and cosine functions are NEVER greater than 1.
 
Subhotosh Khan said:
Valentas said:
Well guys I haven't been at school when teacher was explaining quations like this:

(cos5x - 5)(5sin5x - 2.5)=0

I may use the rule: one multiplicative must be zero

E.G. cos5x - 5=0 and 5sin5x - 2.5=0

I think I should get 2 solutions but in the answers there is only one. If you don't know what I'm talking about, please solve this on your method :)

another equation: ctgx(2 - cosx)=0

I get the idea that cosx=0 -----> x= pi/2 + npi

but what to do with 2 - cosx ? again only one answer above x= :)
Click to expand...

You have to remember:

|cos(?)| ? 1

and

|sin(?)|? 1

That is the magnitudes of the sine and cosine functions are NEVER greater than 1.
Click to expand...


Thank you my friend. I have learned that like one year ago. Thank you for reminder.
 
Cannot think of a good come back right now ..... but I'll get you .....
 
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