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[主观题]
Is this the ______ that you are late again? ()A.seasonB.causeC.reasonD.excuse
Is this the ______ that you are late again? ()
A.season
B.cause
C.reason
D.excuse
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Is this the ______ that you are late again? ()
A.season
B.cause
C.reason
D.excuse
已知f1(t)=tε(t),f2(t)=ε(t)-ε(t-2),求y(t)=f1(t)*f2(t-1)*δ'(t-2)。
A.mightn't
B.won't
C.needn't
D.mustn't
A.y’(t)/x(t)
B.-y’(t)/x(t)
C.y’(t)/x’(t)
D.y(t)/x’(t)
E.-y(t)/x’(t)
求下列函数的卷积积分f1(t)*f2(t): (1)f1(t)=tε(t),f2(t)=ε(t); (3)f1(t)=f2(t)=e-2tε(t); (5)f1(t)=tε(t),f2(t)=e-2tε(t); (7)f1(t)=ε(t)一ε(t一4),f2(t)=sin(πt)ε(t); (9)f1(t)=tε(t一1),f2(t)=ε(t+3);