Show that ##2 {\cos \theta} +(1- \tan \theta)^2≈ 3 - 2\theta##

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The discussion revolves around solving the equation 2 cos θ + (1 - tan θ)² ≈ 3 - 2θ, emphasizing the importance of small angle approximations. Participants note that for small θ, cos θ can be approximated as 1 - (1/2)θ² and tan θ as θ. The solution involves analyzing the coefficients of different powers of θ, leading to a conclusion that the terms can be separated into even and odd functions. There is a consensus that the problem assumes θ is small, which simplifies the calculations. The conversation highlights the need for clarity regarding the assumption of small angles in the initial problem statement.
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Homework Statement
Show that ##2 \cos \theta +(1- \tan \theta)^2≈ 3 - 2\theta##
Relevant Equations
trigonometry
This is a past paper question...

find the solution here from ms
1645159566726.png
...wawawawawa...it took a little bit of my time because i was only thinking of taking limits...then realized that i was wrong as we have to remain with ##2θ##...i later realized that for small approximations, ##\cos θ≈1-\frac {1}{2}θ^2, \tan θ≈θ##.

Is there a different way of solving this problem?
 
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Term order of 1 comes as 2+1=3
Coefficient of ##\theta## comes as 0-2=-2
Coefficient of ##\theta^2## comes as -1+1=0
Coefficient of ##\theta^3## comes as 0+0=0
and so on.

When we write the formula
[2\ cos\theta+\sec^2\theta]+[-2\tan\theta]
=[even function of ##\theta##]+[odd function of ##\theta##]
All the even power terms come from the first term. All the odd power terms come from the second term and it is easy to get.
 
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This is the continuation of the question...part (b)... i really am not getting how they are solving this...the angles are in radians...approximation is their approach...

1645187085927.png


solution;

1645187131484.png


any better way?
 
chwala said:
any better way?
I doubt it. In this part, as in the first part, they're assuming that ##\theta## is reasonably small, so ##\sin(\theta) \approx \theta##.

Using the result of the first part of the problem, we have ##3 - 2 \theta = 28\sin(\theta) \approx 28\theta##. The result follows almost immediately.
 
Mark44 said:
I doubt it. In this part, as in the first part, they're assuming that ##\theta## is reasonably small, so ##\sin(\theta) \approx \theta##.

Using the result of the first part of the problem, we have ##3 - 2 \theta = 28\sin(\theta) \approx 28\theta##. The result follows almost immediately.
Noted ...cheers Mark.
 
chwala said:
This is the continuation of the question...part (b)... i really am not getting how they are solving this...the angles are in radians...approximation is their approach...

View attachment 297267

It would have been helpful to include, in Post #1, a statement about θ being a small angle.
 
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