题目

已知函数f(x)=ax2+bcosx+sinx-1满足f()=5,则f()的值是（    ） A.5-                                 B.-5 C.4                                        D.-4 答案：解析：∵f()=a()2+bcos+sin-1=5,∴f()=a()2+bcos()+sin()-1=a()2+bcos-sin-1=a()2+bcos+sin-1-2sin=5-2×=4.答案：C

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