# When should I set + , - or ±

Trigonometry equalities, inequalities and expressions - sin, cos, tan, cot

### When should I set + , - or ±

Hello my name is Charin. I cant work out when should i set + , - or ±
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Example:
Give is tan(v)=7/24 Determine relevancy for Sin(v),Cos(v) and Cot(v).

Solution :

sin=± 7/25 ( why is ±)
Cos=± 24/25 ( why is ±)

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charin79

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Joined: Mon Mar 10, 2008 12:24 am
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it is ±
because
when we solve the problem we have:

(sinx)2 = a

where a is some number.

and then we have:

sin x = ±√a

Math Tutor

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Joined: Sun Oct 09, 2005 11:37 am
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### Re: when should i set + , - or ±

charin79 wrote:Hello my name is Charin. I cant work out when should i set + , - or ±
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Example:
Give is tan(v)=7/24 Determine relevancy for Sin(v),Cos(v) and Cot(v).

Solution :

sin=± 7/25 ( why is ±)
Cos=± 24/25 ( why is ±)

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Using some following mathematical formulas:

$$1+tan^2x=\frac1{cos^2x} => cosx=\pm\sqrt{\frac1{1+tan^2x}}$$

$$sin^2x+cos^2x=1 => sinx=\pm\sqrt{1-cos^2x}$$

$$tanx.cotx=1 =>cotx=\frac1{tanx}$$

dduclam

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Location: HUCE-Vietnam
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### Re: when should i set + , - or ±

Well i have a triangle and the hyp is 15 and one of the angles is 68 one is 90. I dint know how to get another side with just that. Could you help me?

Hybride DeViL

caydaAtes

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Joined: Sat Jan 03, 2015 2:24 am
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### Re: When should I set + , - or ±

The non-hypotenuse side adjacent to the angle of 68 is of length "15 cos 68".
The side opposite to the angle of 68 is of length "15 sin 68".

This follows from the definitions of sin and cos:
sin angle = Opposite / Hypotenuse
cos angle = Adjacent / Hypotenuse
We know the angle and the hypotenuse, so we can re-arrange the equations to get the lengths of the opposite and adjacent sides.

http://www.mathsisfun.com/sine-cosine-tangent.html

Hope this helped,

R. Baber.
Guest

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