Using Trigonometric Identities

**vaironxxrd** · January 20th 2013, 01:44 PM

Hello Everyone,

I have the following instruction, "Use trigonometric identities to transform one side of the equation into the other" ?

First I don't exactly understand what the instructions are saying.

The problem is as follows

cos Θ sec Θ = 1

The book gives me the solution which is

cos Θ sec Θ = 1 $\frac{1}{sec Θ}$ = 1

( 0 < Θ < π/2) (I guess this means Θ is an acute angle)

**Plato** · January 20th 2013, 02:58 PM

Originally Posted by vaironxxrd

I have the following instruction, "Use trigonometric identities to transform one side of the equation into the other" ? First I don't exactly understand what the instructions are saying. The problem is as follows
cos Θ sec Θ = 1
The book gives me the solution which is
cos Θ sec Θ = 1 $\frac{1}{sec Θ}$ = 1
( 0 < Θ < π/2) (I guess this means Θ is an acute angle)

If the question is to solve for $\theta$ in the equation $\cos(\theta)\sec(\theta)=1$ then the answer given makes no sense.
Because the solution is $\forall\theta\left[\theta\ne\frac{(2n+1)\pi}{2}\right]$ .

On the other hand, did the statement begin with restrictions on $\theta~?$

**vaironxxrd** · January 20th 2013, 03:42 PM

Originally Posted by Plato

If the question is to solve for $\theta$ in the equation $\cos(\theta)\sec(\theta)=1$ then the answer given makes no sense.
Because the solution is $\forall\theta\left[\theta\ne\frac{(2n+1)\pi}{2}\right]$ .

On the other hand, did the statement begin with restrictions on $\theta~?$

The book first gives the instruction, "transform one side of the equation into the other" (Which doesn't make any sense to me)
It also doesn't provide any specific angle it just states the following $( 0 < \theta < \pi/2)$

The actual problem to be solved is...
$cos \theta sec \theta = 1$

The solution is...
"Simplify the expression on the left-hand side of the equation until you obtain the right side"
$cos\theta sec\theta$ = $\frac{1}{sec\theta}\cdot sec\theta$ = 1

**Plato** · January 20th 2013, 04:17 PM

Originally Posted by vaironxxrd

The book first gives the instruction, "transform one side of the equation into the other" (Which doesn't make any sense to me)
It also doesn't provide any specific angle it just states the following $( 0 < \theta < \pi/2)$

The actual problem to be solved is...
$cos \theta sec \theta = 1$

The solution is...
"Simplify the expression on the left-hand side of the equation until you obtain the right side"
$cos\theta sec\theta$ = $\frac{1}{sec(\theta})\cdot sec\theta$ = 1

Well your reply confuses me.

It is absolutely true that if $0<\theta<\frac{\pi}{2}$ then $\cos(\theta)\sec(\theta)=1$ .

So what is the big deal?

**vaironxxrd** · January 20th 2013, 04:36 PM

Originally Posted by Plato

Well your reply confuses me.

It is absolutely true that if $0<\theta<\frac{\pi}{2}$ then $\cos(\theta)\sec(\theta)=1$ .

So what is the big deal?

All the instructions given are to "Use trigonometric identities to transform one side of the equation into the other".
I myself am confused on where to start

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