[紧急求助,已知a为第二象限角,sin(派-a)=24/25,则cos a/2的值为?辛苦 又问...已知a为第二象限角,sin(派-a)=24/25,则cos a/2的值为?
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[紧急求助,已知a为第二象限角,sin(派-a)=24/25,则cos a/2的值为?辛苦 又问...已知a为第二象限角,sin(派-a)=24/25,则cos a/2的值为?
[紧急求助,已知a为第二象限角,sin(派-a)=24/25,则cos a/2的值为?辛苦 又问...
已知a为第二象限角,sin(派-a)=24/25,则cos a/2的值为?
[紧急求助,已知a为第二象限角,sin(派-a)=24/25,则cos a/2的值为?辛苦 又问...已知a为第二象限角,sin(派-a)=24/25,则cos a/2的值为?
sina=24/25
cosa=-7/25
π/2
sin(π-a)=sin a=24/25
cos a/2=±√[(sin a+1)/2]=±√(49/50)=±7√2/10
因为a为第二象限角,所以cos a/2=-7√2/10
sin(pi-a)=sina=24/25
cosa=-7/25(a为第二象限角)(7^2+24^2=25^2)
cosa=2cos^2(a/2)-1
cos(a/2)=3/5
sin(π-a)=sina=24/25
a为第二象限角
cosa=-7/25
sina=24/25>√2/2=sin3π/4
即π/2π/4即a/2是第一象限角
cosa=2(cosa/2)^2-1
-7/25=2(cosa/2)^2-1
cosa/2=±3/5
综上cosa/2=3/5