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下列各式中,与是同类二次根式的是( ) A. B. C. D.
下列各式中,与
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是同类二次根式的是( )
A.
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B.
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C.
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D.
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考点分析:
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已知x=-1是方程x
2+mx=0的一个实数根,则m的值是( )
A.0
B.1
C.2
D.-2
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下列7个数
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,3.1415926,(π-2)
,-3,
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,-
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,0 中,有理数有( )个.
A.4
B.2
C.3
D.5
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观察与思考:阅读下列材料,并解决后面的问题.
在锐角△ABC中,∠A、∠B、∠C的对边分别是a、b、c,过A作 AD⊥BC于D(如图1),则sinB=
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,sinC=
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,即AD=csinB,AD=bsinC,于是csinB=bsinC,即
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.同理有:
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,
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,所以
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即:在一个三角形中,各边和它所对角的正弦的比相等.在锐角三角形中,若已知三个元素(至少有一条边),运用上述结论和有关定理就可以求出其余三个未知元素.根据上述材料,完成下列各题.
(1)如图2,△ABC中,∠B=45°,∠C=75°,BC=60,则∠A=______;AC=______
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