Express 3cosx+3sinx in the form Rcos(x-a)

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Homework Help Overview

The problem involves expressing the trigonometric expression 3cosx + 3sinx in the form Rcos(x-a) and determining conditions under which a related function T(x) is undefined, as well as finding specific values of x that satisfy an equation involving T(3x).

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the transformation of the expression into the desired form and question the conditions under which the function T(x) is undefined. There are attempts to clarify the steps needed for both parts of the problem, particularly focusing on the implications of the denominator being zero.

Discussion Status

There is an ongoing exploration of the problem with participants providing guidance on how to approach parts (a) and (b). Some participants are clarifying the conditions for the function's definition and the correct substitution process for T(3x). Multiple interpretations of the steps are being discussed without reaching a consensus.

Contextual Notes

Participants are navigating the constraints of the problem, particularly the requirement that R must be positive and the angle a must lie within a specific range. There is also a focus on ensuring clarity in the definitions and expressions used in the problem.

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Homework Statement



(i) Express 3cosx+3sinx in the form Rcos(x-a) where R>0 and 0<a<(1/2)∏

(ii) The expression T(x) is definded by T(x)=8/(3cosx+3sinx)

(a) Determine a value of x for which T(x) is not defined

(b) Find the smallest positive value of x satisfying T(3x)=(8/9)√6 giving your answer in exact form.

The Attempt at a Solution



for (i) 3√2cos(x-(1/4)∏)

(a) 8/(3√2cos(x-(1/4)∏)). Could someone explain how to do (a) and (b) please in terms I can understand easy. Thanks.
 
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Hi studentxlol! :smile:

To do (a) you need to consider when a function is not defined.
In particular, when is that the case when dividing?

To do (b) you first need to substitute T(3x) in the equation.
Can you do that?
 
I like Serena said:
Hi studentxlol! :smile:

To do (a) you need to consider when a function is not defined.
In particular, when is that the case when dividing?

To do (b) you first need to substitute T(3x) in the equation.
Can you do that?

(a) You can't divide a function when its denominator is 0 so 8/ 3cosx+3sinx can't equal 0 right?

(b) Substitute T(3x)=(8/9)√6 into 3(8/(3cosx+3sinx) right?

?
 
studentxlol said:
(a) You can't divide a function when its denominator is 0 so 8/ 3cosx+3sinx can't equal 0 right?

Yes, but only the denominator can't equal 0 (which is not the expression you just wrote).
studentxlol said:
(b) Substitute T(3x)=(8/9)√6 into 3(8/(3cosx+3sinx) right?

?

It's the other way around.
Start with T(x)=8/(3cosx+3sinx).
Now replace every occurrence of "x" by "3x".
 
Last edited:

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