滿足條件cosαcosβ-sinαsinβ=1/2的角α、β不可能是A. α=11π/12 β=7π/12 B. α=π/12 β=π/4 C. α=π/2 β=π/4 D. α=7π/4 β=25π/12
熱心網(wǎng)友
由cosαcosβ-sinαsinβ=1/2，得cos(α+β)=1/2.∴α+β=2nπ±π/3.(n為整數(shù))∴A、C、D都不可能.
滿足條件cosαcosβ-sinαsinβ=1/2的角α、β不可能是A. α=11π/12 β=7π/12 B. α=π/12 β=π/4 C. α=π/2 β=π/4 D. α=7π/4 β=25π/12
由cosαcosβ-sinαsinβ=1/2，得cos(α+β)=1/2.∴α+β=2nπ±π/3.(n為整數(shù))∴A、C、D都不可能.