f(x)=ax^2+x-ln(x+1),a∈R,x>-1,
f'(x)=2ax+1-1/(x+1)
=x(2ax+2a+1)/(x+1),
a=0时f'(x)=x/(x+1),-10,f(x)是增函数.
a≠0时f'(x)=2ax[x+(2a+1)/(2a)]/(x+1),
a>0时-10,f(x)是增函数.
a-1,由序轴标根法,x>0或-10,f(x)是增函数.
整合(略).
f(x)=ax^2+x-ln(x+1),a∈R,x>-1,
f'(x)=2ax+1-1/(x+1)
=x(2ax+2a+1)/(x+1),
a=0时f'(x)=x/(x+1),-10,f(x)是增函数.
a≠0时f'(x)=2ax[x+(2a+1)/(2a)]/(x+1),
a>0时-10,f(x)是增函数.
a-1,由序轴标根法,x>0或-10,f(x)是增函数.
整合(略).