灵鹊做题网请教一题高一三角函数题
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请教一题高一三角函数题
已知π/4
已知π/4
sin(3π/4+b)=sin(b-π/4),sin(a+b)=sin(π/4+a+b-π/4)=sin(π/4+a)cos(b-π/4)+cos(π/4+a)sin(b-π/4)
sin(π/4+a)=根号下(1-9/25),a+π/4在第2象限,取正得4/5
cos(b-π/4)=根号下(1-25/169),b-π/4在第4象限,取正得12/13
sin(a+b)=sin(π/4+a+b-π/4)=sin(π/4+a)cos(b-π/4)+cos(π/4+a)sin(b-π/4)=
48/65-15/65=33/65
sin(π/4+a)=根号下(1-9/25),a+π/4在第2象限,取正得4/5
cos(b-π/4)=根号下(1-25/169),b-π/4在第4象限,取正得12/13
sin(a+b)=sin(π/4+a+b-π/4)=sin(π/4+a)cos(b-π/4)+cos(π/4+a)sin(b-π/4)=
48/65-15/65=33/65