Question #cd107

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Answer 1 · 2015-01-31T23:55:52

Let's first draw a triangle to get the trigonometry right.

enter image source here
We'll use $∠ A$ $angleA$ instead of $x$ $x$ because of the picture

$cos A$ $cosA$ is defined as $b / h$ $b//h$
$tan A$ $tanA$ is defined as $a / b$ $a//b$

So we get: $cosA*tanA=cancelb/h * a/cancelb=a/h$

Which is the definition of the sine .

Answer :
$cosA*tanA=sinA$

Extra
You could have done this another way if you knew that

$tanA=sinA/cosA$

Then it would be:

$cosA*tanA=cancel(cosA)*sinA/cancel(cosA)=sinA$ (same result)

(picture: Wikipedia)

Answer 2 · 2017-11-07T15:40:09

$cosx tanx -= sinx$

$cosx tanx -= cosx * sinx/cosx -= sinx$