Solve-1-cos-70-2-cos-10-

Question Number 106493 by mohammad17 last updated on 05/Aug/20

S o l v e ?

(1) c o s (70)

(2) c o s (10)

Commented by malwaan last updated on 05/Aug/20

c o s 10 = c o s 70 + c o s 50

Answered by bemath last updated on 05/Aug/20

consider \cos 3 x = 4 \cos^{3} x - 3 \cos x

put x = 10 °

\cos 30 ° = {4 \cos}^{3} 10 ° - 3 \cos 10 °

\frac{\sqrt{3}}{2} = 4 \cos^{3} 10 ° - 3 \cos 10 °

solve via Cardano method

Commented by mohammad17 last updated on 05/Aug/20

s i r c a n y o u g i v e b e r a w t h e C a r d a n o m e t h o d

Commented by malwaan last updated on 06/Aug/20

I s o l v e d i t b y t r i g o n o m i t r i c

m e t h o d a n d g e t t h e s o l u t i o n s

c o s 10; - c o s 70; - c o s 50

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