lim f(x)/(x-1)=1.5 而不是无穷,说明当x→1时,f(x)→0.
而f(x)在x=1处可导,则f(1)=0
则 lim f(x)/(x-1)= lim[ f(x) -0]/(x-1) = lim[ f(x) - f(1)]/(x-1)
= y'(1)
即
dy|x=1 =1.5
lim f(x)/(x-1)=1.5 而不是无穷,说明当x→1时,f(x)→0.
而f(x)在x=1处可导,则f(1)=0
则 lim f(x)/(x-1)= lim[ f(x) -0]/(x-1) = lim[ f(x) - f(1)]/(x-1)
= y'(1)
即
dy|x=1 =1.5