求下列各式的值 cos3分之25π=tan（-4分之15π） sin810°+tan765°-cos360°
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cos(25π/3) = cos(8π+π/3) = cos(π/3) = 1/2 ；
tan(-15π/4) = tan(-4π+π/4) = tan(π/4) = 1 ；
sin810°+tan765°-cos360°
= sin(720°+90°)+tan(720°+45°)-cos0°
= sin(90°)+tan(45°)-1
= 1+1-1
= 1 .
tan(-15π/4) = tan(-4π+π/4) = tan(π/4) = 1 ；
sin810°+tan765°-cos360°
= sin(720°+90°)+tan(720°+45°)-cos0°
= sin(90°)+tan(45°)-1
= 1+1-1
= 1 .
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