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

$$Solve?$$$$\left(1\right)cos\left(70\right)$$$$\left(2\right)cos\left(10\right)$$

Commented by malwaan last updated on 05/Aug/20

$$cos10=cos70+cos50$$

Answered by bemath last updated on 05/Aug/20

$$\mathrm{consider}\cos 3\mathrm{x}=4\cos {}^3\mathrm{x}-3\cos \mathrm{x}$$$$\mathrm{put}\mathrm{x}=10°$$$$\cos 30°={4\cos }^{3}10°-3\cos 10°$$$$\frac{\sqrt{3}}{2}=4\cos {}^{3}10°-3\cos 10°$$$$\mathrm{solve}\mathrm{via}\mathrm{Cardano}\mathrm{method}$$

Commented by mohammad17 last updated on 05/Aug/20

$$sircanyougiveberawtheCardanomethod$$

Commented by malwaan last updated on 06/Aug/20

$$Isolveditbytrigonomitric$$$$methodandgetthesolutions$$$$cos10;-cos70;-cos50$$

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