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fomenos
3 years ago
8

How do I prove that 2 cot 2x = cot x-tan x?

Mathematics
1 answer:
BlackZzzverrR [31]3 years ago
7 0
We will start off working on the right hand side. 
<span>cot x - tan x </span>
<span>= [cos x / sin x] - [sin x / cos x] </span>
<span>= [(cos x)^ 2 - (sin x)^2] / [sin x cos x] </span>

<span>This is where it gets a bit tougher if you do not have your formula list with you. </span>
<span>(cos x)^ 2 - (sin x)^2 = cos(2x) </span>
<span>sin 2x = 2 sin x cos x </span>

<span>Note that by arranging the second formula, we will have sin x cos x = (1/2) sin 2x </span>

<span>Hence, we will get: </span>
<span>[(cos x)^ 2 - (sin x)^2] / [sin x cos x] </span>
<span>= [cos 2x] / (1/2)[sin 2x] </span>
<span>= 2[cos 2x] / [sin 2x] </span>
<span>= 2cot 2x </span>
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