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三角形的两边分别为3cm,5cm,其所夹角的余弦为方程5x2-7x-6=0的根,...
三角形的两边分别为3cm,5cm,其所夹角的余弦为方程5x2-7x-6=0的根,则这个三角形的面积是 cm2.
考点分析:
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②当且仅当x=2kл+
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,k∈Z时,f(x)<0.
其中正确的是( )
A.①②
B.②③
C.③
D.④
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是任意三个非零向量,且互不共线,有下列四个命题:
①(
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).
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-(
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.
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).
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=
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; ②|
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|≤|
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|+|
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③(
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.
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).
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).
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2.
其中真命题的有( )个.
A.1
B.2
C.3
D.4
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