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- JOHNLv 77 years agoFavourite answer
A is in the 4th quadrant from the info given. So A=7π/4. Verify: sin(7π/4)=sin (2π-π/4)=sin2πcosπ/4-cos2πsinπ/4=

-sinπ/4=

-1/√2, cos(7π/4)=cos(2π-π/4)=

cos2πcosπ/4+sin2πsinπ/4=cosπ/4=1/√2.

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