已知tanα=-1/3,求下列各式的值 (1)2sin^2-3/2sinαcosα+5cos^α (2)1/1-sinαcosα已知tanα=-1/3,求下列各式的值(1)2sin^2-3/2sinαcosα+5cos^α(2)1/1-sinαcosα2sin^2-3/2sinαcosα+5cos^2α
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![已知tanα=-1/3,求下列各式的值 (1)2sin^2-3/2sinαcosα+5cos^α (2)1/1-sinαcosα已知tanα=-1/3,求下列各式的值(1)2sin^2-3/2sinαcosα+5cos^α(2)1/1-sinαcosα2sin^2-3/2sinαcosα+5cos^2α](/uploads/image/z/2738636-44-6.jpg?t=%E5%B7%B2%E7%9F%A5tan%CE%B1%3D-1%2F3%2C%E6%B1%82%E4%B8%8B%E5%88%97%E5%90%84%E5%BC%8F%E7%9A%84%E5%80%BC+%EF%BC%881%EF%BC%892sin%5E2-3%2F2sin%CE%B1cos%CE%B1%2B5cos%5E%CE%B1+%EF%BC%882%EF%BC%891%2F1-sin%CE%B1cos%CE%B1%E5%B7%B2%E7%9F%A5tan%CE%B1%3D-1%2F3%2C%E6%B1%82%E4%B8%8B%E5%88%97%E5%90%84%E5%BC%8F%E7%9A%84%E5%80%BC%EF%BC%881%EF%BC%892sin%5E2-3%2F2sin%CE%B1cos%CE%B1%2B5cos%5E%CE%B1%EF%BC%882%EF%BC%891%2F1-sin%CE%B1cos%CE%B12sin%5E2-3%2F2sin%CE%B1cos%CE%B1%2B5cos%5E2%CE%B1)
已知tanα=-1/3,求下列各式的值 (1)2sin^2-3/2sinαcosα+5cos^α (2)1/1-sinαcosα已知tanα=-1/3,求下列各式的值(1)2sin^2-3/2sinαcosα+5cos^α(2)1/1-sinαcosα2sin^2-3/2sinαcosα+5cos^2α
已知tanα=-1/3,求下列各式的值 (1)2sin^2-3/2sinαcosα+5cos^α (2)1/1-sinαcosα
已知tanα=-1/3,求下列各式的值
(1)2sin^2-3/2sinαcosα+5cos^α
(2)1/1-sinαcosα
2sin^2-3/2sinαcosα+5cos^2α
已知tanα=-1/3,求下列各式的值 (1)2sin^2-3/2sinαcosα+5cos^α (2)1/1-sinαcosα已知tanα=-1/3,求下列各式的值(1)2sin^2-3/2sinαcosα+5cos^α(2)1/1-sinαcosα2sin^2-3/2sinαcosα+5cos^2α
(1)
2sin²α-3/2sinαcosα+5cos²α
=(2sin²α-3/2sinαcosα+5cos²α)/(sin²α+cos²α)
=(2tan²α-3/2 tanα+5)/(tan²α+1) 【分子分母同时处以cos²α】
=[2×(-1/3)²-3/2 ×(-1/3)+5]/[(-1/3)²+1]
=(2/9+1/2+5)/(1/9+1)
=133/20
(2)
1/(1-sinαcosα)
=(sin²α+cos²α)/(sin²α+cos²α-sinαcosα)
=(tan²α+1)/(tan²α+1-tanα) 【分子分母同时乘以cos²α】
=[(-1/3)²+1]/[(-1/3)²+1-(-1/3)]
=(10/9)/(13/9)
=10/13