1.已知sin(π/4-α)=3/5,π/4-α为第二象限角,求sin(α-13π/4)+sin(α+21π/4)的值2.已知y=a-bcos(3x-π/2的最大值为6,最小值为-2,求实数a,b的值
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![1.已知sin(π/4-α)=3/5,π/4-α为第二象限角,求sin(α-13π/4)+sin(α+21π/4)的值2.已知y=a-bcos(3x-π/2的最大值为6,最小值为-2,求实数a,b的值](/uploads/image/z/10141456-40-6.jpg?t=1.%E5%B7%B2%E7%9F%A5sin%28%CF%80%2F4-%CE%B1%29%3D3%2F5%2C%CF%80%2F4-%CE%B1%E4%B8%BA%E7%AC%AC%E4%BA%8C%E8%B1%A1%E9%99%90%E8%A7%92%2C%E6%B1%82sin%28%CE%B1-13%CF%80%2F4%29%2Bsin%28%CE%B1%2B21%CF%80%2F4%EF%BC%89%E7%9A%84%E5%80%BC2.%E5%B7%B2%E7%9F%A5y%3Da-bcos%283x-%CF%80%2F2%E7%9A%84%E6%9C%80%E5%A4%A7%E5%80%BC%E4%B8%BA6%2C%E6%9C%80%E5%B0%8F%E5%80%BC%E4%B8%BA-2%2C%E6%B1%82%E5%AE%9E%E6%95%B0a%2Cb%E7%9A%84%E5%80%BC)
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1.已知sin(π/4-α)=3/5,π/4-α为第二象限角,求sin(α-13π/4)+sin(α+21π/4)的值2.已知y=a-bcos(3x-π/2的最大值为6,最小值为-2,求实数a,b的值
1.已知sin(π/4-α)=3/5,π/4-α为第二象限角,求sin(α-13π/4)+sin(α+21π/4)的值
2.已知y=a-bcos(3x-π/2的最大值为6,最小值为-2,求实数a,b的值
1.已知sin(π/4-α)=3/5,π/4-α为第二象限角,求sin(α-13π/4)+sin(α+21π/4)的值2.已知y=a-bcos(3x-π/2的最大值为6,最小值为-2,求实数a,b的值
1
sin(π/4-α)=3/5
π/4-α为第二象限角
cos(π/4-α)=-根号[1-sin^2(π/4-α)]=-根号[1-(3/5)^2] = -4/5
sin(α-13π/4)+sin(α+21π/4)
=sin(-4π+π+α-π/4)+sin(4π+π+α+π/4)
=sin(π+α-π/4)+sin(π+α+π/4)
=-sin(α-π/4)-sin(α+π/4)
=sin(π/4-α)-cos(π/2-α-π/4)
=sin(π/4-α)-cos(π/4-α)
=3/5-(-4/5)
=8/5
2.
y=a-bcos(3x-π/2)
-1≤ cos(3x-π/2) ≤ 1
当b>0时:
最小值a-b=-2,最大值a+b=6
a=2,b=4
当b<0时:
最小值a+b=-2,最大值a-b=6
a=2,b=-4
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