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The expression cot(theta) x sec(theta) is equivalent to a) cos(theta) / sin^2(theta) b)...

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mrcoolguy555 | Student, College Freshman | (Level 1) Honors

Posted March 20, 2012 at 8:52 AM via web

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The expression cot(theta) x sec(theta) is equivalent to

a) cos(theta) / sin^2(theta)

b) sin(theta) 

I am pretty sure these are trig proofs. But I can't figure them out, a quick thoroughly described answer would be great.

Thanks

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embizze | High School Teacher | (Level 1) Educator Emeritus

Posted March 20, 2012 at 10:47 AM (Answer #1)

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We are given the expression `cot theta*sec theta` :

Expressing these in terms of sin and cos yields:

`costheta/sintheta*1/costheta`

This product is `1/sintheta=csctheta`

So neither (a) nor (b) are correct simplifications or identities since

(a) `costheta/(sin^2theta)=cottheta*1/sintheta=cottheta*csctheta` and

(b) `sintheta`

are neither equivalent to `cotthetasectheta` .

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rcmath | High School Teacher | (Level 1) Associate Educator

Posted March 20, 2012 at 10:50 AM (Answer #2)

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Mathematically your statements are incorrect. Let's invetigate one at a time.

a)`costheta/(sin^2theta)=`

`costheta/[sintheta*sintheta]=`

`costheta/sintheta*1/sintheta=`

`cottheta*csctheta`

In general csc of an angle is not equal to the sec of that angle. They are equal if `theta=45+nPi`

b)`cottheta*sectheta=`

`costheta/sintheta*1/costheta=1/sintheta` when `costheta!=0, theta!=Pi/2+nPi`

Here also in general `1/sintheta!=sintheta`

 

 

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