非常感谢各位大神在高数考试中借用这四道题。
16
= 2sin？(x/2)/[2xsin(x/2)cos(x/2)]
= sin(x/2)/[xcos(x/2)]
=(1/2)sin(x/2)/[(x/2)cos(x/2)]
极限是1/2
17.
y ' =[e^(-x/2)](-1/2)cos3x+[e^(-x/2)](-sin3x)*3
=-[(1/2)cos3x+3sin3x][e^(-x/2)]
18.
= -(1/2)∫[e^(-x？)]d(-x？)
= (-1/2)e^(-x？)|
= (e - 1/e)/2
19.
= ∫(√x - x？)dx
= [(2/3)x^(3/2) - x？/3)|
= 2/3 - 1/3
= 1/3