cos20*cos70-sin20*sin70cos20°*cos70°-sin20°*sin70°= 1+tan15/1-tan15°=sin72°*cos18°+cos72°*sin18°=tan12°+tan33/1-tan12°*tan33°=已知cosθ=—3/5 θ∈(π/2,π),求sin(θ+π/3)的值sin15°*cos15°=cos²π/8—sin²π/8=tan22.5°/1—tan²22.5°=2cos²22.5°—1=sin(—7π/12)=cos(—61π/12)=tan35π/12=已知cosa/8=—4/5,8π大神们顺便把过程也附上吧.......

问题描述:

cos20*cos70-sin20*sin70
cos20°*cos70°-sin20°*sin70°=
1+tan15/1-tan15°=
sin72°*cos18°+cos72°*sin18°=
tan12°+tan33/1-tan12°*tan33°=
已知cosθ=—3/5 θ∈(π/2,π),求sin(θ+π/3)的值
sin15°*cos15°=
cos²π/8—sin²π/8=
tan22.5°/1—tan²22.5°=
2cos²22.5°—1=
sin(—7π/12)=
cos(—61π/12)=
tan35π/12=
已知cosa/8=—4/5,8π
大神们顺便把过程也附上吧.......

1.=cos(20°+70°)=cos90°=0
2.上下同时×cos15°,原式=(cos15°+sin15°)/(cos15°-sin15°)=cos30°/cos60°=根号3
3.原式=tan(12°+33°)=tan45°=1
4.原式=sinθcosπ/3+cosθsinπ/3=带入就能算到
5.1/2sin30°=1
6.原式=cosπ/4=根号2/2
7.原式=tan45°=1
8.2cos²22.5°—1=cos45°=根号2/2
9.sin(—7π/12)=sin(-3π/12-4π/12)=公式拆开自己算
10.cos(—61π/12)=cos(11π/12)=-cos(π/12)=-cos(4π/12-3π/12)=公式拆开自己算
11.tan35π/12=tan(-π/12)=-tan(4π/12-3π/12)=公式拆开自己算
12.
13.这都是公式吧?看着书上和差角公式带入就算出来了

cos20°*cos70°-sin20°*sin70°=cos(20°+70°)=cos(90°)=0已知sinx=—3/5,x是第四象限角,求sin(π/4—x)cos(π/4+x),tan(x—π/4)的值cosx=4/5 (因为x是第四象限)sin(π/4—x)=sin π/4 cosx-cosπ/4 si...