Trigonometric Ratios of Angle \(\frac{A}{3}\)

We will learn about the trigonometric ratios of angle \(\frac{A}{3}\) in terms of angle A. 

How to express sin A, cos A and tan A in terms of \(\frac{A}{3}\)?

(i) For all values of the angle A we know that, sin 3A = 3 sin A - 4 sin\(^{3}\) A

Now replacing A by \(\frac{A}{3}\) in the above relation then we obtain the relation as,

sin A = 3 sin \(\frac{A}{3}\) - 4 sin\(^{3}\) \(\frac{A}{3}\)


(ii) For all values of the angle A we know that, cos 3A= 4 cos\(^{3}\) A - 3 cos A

Now replacing A by \(\frac{A}{3}\) in the above relation then we obtain the relation as,

cos A = 4 cos\(^{3}\) \(\frac{A}{3}\) - 3 cos \(\frac{A}{3}\)


(iii) For all values of the angle A we know that, tan 3A = \(\frac{3  tan  A  -  tan^{3}  A}{1  -  3  tan^{2}  A}\)

Now replacing A by \(\frac{A}{3}\) in the above relation then we obtain the relation as,

tan A = \(\frac{3  tan  \frac{A}{3}  -  tan^{3}  \frac{A}{3}}{1  -  3  tan^{2}  \frac{A}{3}}\)

















11 and 12 Grade Math

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