.计算:.
(每小题5分,本题共20分)计算:(1) (2)(-+-)×(-48)(3)(4)
(本题6分)(1)已知:sinα·cos60°=,求锐角α.(2)计算:.
计算与化简:(第(1)(2)(3)题每题4分,第(4)题6分,共18分)(1) 计算:-2×(-3)+(-48)÷6;(2)计算: (3)化简:;(4)先化简,再求值:其中a=2,b=-1
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