❀ The acute angle between the terminal side and the X - axis is called the basic acute angle.
❀ The basic acute angle is a positive acute angle.
❀ X-axis ႏွα့္ terminal side αΎαားαြα္ αွိေαာ ေαာα့္α်α₯္းαို basic acute angle αု ေαααα္။
❀ basic acute angle αို α‘ေαါα္းေαာα့္ α‘ျαα
္ α‘αΏαဲαα္αွα္αα္။
❀ ေα‘ာα္αါα₯ααာα်ားαို αΎαα့္αါ။
αα္αွα္αားေαာ (ေαးαားေαာ) ေαာα့္αို principal angle αုေαααα္။
Principal Angle ၏ trigonometric ratios α်ား αွာαα္
➤ principal angle αို coordinate system (cartesian plane) αြα္ ေααာα်αါ။
➤ αα္αိုα္ေαာ basic acute angle αို αွာαါ။
➤ basic acute angle ၏ sin ratio ႏွα့္ cos ratio αို αွာαါ။ (sin ႏွα့္ cos αို αိαွ်α္ α်α္ေαာα‘α်ိဳးα်ားαို α‘αြα္ααူ αိႏိုα္αါαα္။)
➤ principal angle ႏွα့္ ၎ႏွα့္αα္αိုα္ေαာ basic acute angle αိုα၏ trigonometric ratio α်ားαα္ αိα္းααα္းααာα α‘ားျαα့္ (numerically) αူαီαΎααါαα္။
➤ αိုαေαာ္ principal angle ၏ trigonometric ratio α်ားα‘αြα္ αα္αိုα္αာ quadrant ႏွα့္ αိႇ၍ ααα‘αာ αα္αွα္ေαးααါαα္။
Example : Find the six trigonometric ratios of 120°.
$ \displaystyle \ \ \ \text{But }120{}^\circ \ \text{lies in the second quadrand}\text{.}$
$ \displaystyle \therefore \ \sin 120{}^\circ =\sin 60{}^\circ =\frac{{\sqrt{3}}}{2}$
$ \displaystyle \ \ \ \cos 120{}^\circ =-\cos 60{}^\circ =-\frac{1}{2}$
$ \displaystyle \therefore \ \tan 120{}^\circ =-\sqrt{3}$
$ \displaystyle \ \ \ \cot 120{}^\circ =-\frac{{\sqrt{3}}}{3}$
$ \displaystyle \ \ \ \sec 120{}^\circ =-2$
$ \displaystyle \ \ \ \operatorname{cosec}120{}^\circ =-\frac{{2\sqrt{3}}}{3}$
α
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ားα
ွာα
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