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°
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![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°](/uploads/image/z/2495087-71-7.jpg?t=cos20%2Acos70-sin20%2Asin70cos20%C2%B0%2Acos70%C2%B0-sin20%C2%B0%2Asin70%C2%B0%3D+1%2Btan15%2F1-tan15%C2%B0%3Dsin72%C2%B0%2Acos18%C2%B0%2Bcos72%C2%B0%2Asin18%C2%B0%3Dtan12%C2%B0%2Btan33%2F1-tan12%C2%B0%2Atan33%C2%B0%3D%E5%B7%B2%E7%9F%A5cos%CE%B8%3D%E2%80%943%2F5+%CE%B8%E2%88%88%28%CF%80%2F2%2C%CF%80%29%2C%E6%B1%82sin%EF%BC%88%CE%B8%2B%CF%80%2F3%29%E7%9A%84%E5%80%BCsin15%C2%B0%2Acos15%C2%B0%3Dcos%26%23178%3B%CF%80%2F8%E2%80%94sin%26%23178%3B%CF%80%2F8%3Dtan22.5%C2%B0)
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°
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.......
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°
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 sinx
=(根号2/2)(4/5+3/5)
=7根号2/10
cos(π/4+x)
=cosπ/4 cosx -sinπ/4 sinx
=(根号2/2)(4/5+3/5)
=7根号2/10
tanx=sinx/cosx=-3/4
tan(x—π/4)
=(tan x- tanπ/4 )/(1+tanx tanπ/4)
=(-3/4-1)/(1-3/4)
=-7
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...
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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
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