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SupplementaryAnglesConcept

Supplementary angles are anglesthat add up to 180 . We are goingto look at how supplementary anglesare applied in trigonometry. Thepurpose of the supplementaryangles equations is to reduce it to a

trigonometry function with only in

it. For instance, sine = -

sine . It can be clearly seen thatthe trigonometry function (sine)does not change. Let us look at howwe derived the supplementaryangles.

1) Look at the quadrant at which

the lies in. It's in the 3rdquadrant .

2) Then find the sign ( +ve or -ve )

of the sine in the 'ASTC'diagram ( Check it at trig ratio). It isnegative.

3) So, we can easily obtain that

= - sin by adding thenegative sign.

Other supplementary angles cansimilarly be found in this manner. Assuch , it is not necessary tomemorise the supplementary angleformulas by heart. Nevertheless ,wehave provided a list ofsupplementary angles for yourconvenience.

List of Supplementary Angles

sine = sine

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BasicTrigonometry

sine = - sine

sine = - sine

tangent = - tangent

tangent = tangent

tangent = - tangent

cosine = - cosine

cosine = - cosine

cosine = cosine

Trigonometry functions like secantand cosecant are related to thecosine and sine function. Thus theyfollow the same rules. For instance,by looking at the supplementaryangles for cosine, we can tell that

secant = -secant . Thisis the same for cosecant andcotangent which have relations withsine and tangent respectively.

Look at how you can apply thisconcept in examples of provingtrigonometry identities.

You may wish to consider taking alook at complementary angles aswell.

Return to Trigonometry Help or BasicTrigonometry .

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