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已知方程x2-5x+2=0的两个解分别为x1、x2,则x1+x2-x1•x2的值...
已知方程x2-5x+2=0的两个解分别为x1、x2,则x1+x2-x1•x2的值为( )
A.-7
B.-3
C.7
D.3
考点分析:
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,则cosB的值等于( )
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下列运算中,正确的是( )
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B.(a-b)
2=a
2-b
2C.2(a-b)=4a-b
D.(a+b)(a-b)=a
2-b
2
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