f(x) = x|x-5|/[(x-1)(x-5)sinx ]
lim(x->0) x|x-5|/[(x-1)(x-5)sinx ]
=lim(x->0) |x-5|/[(x-1)(x-5) ]
=1
x=0 : 可去间断点 (第1类间断点)
lim(x->5+) x|x-5|/[(x-1)(x-5)sinx ]
=lim(x->5+) x/[(x-1)sinx ]
= 5/(4sin1)
lim(x->5-) x|x-5|/[(x-1)(x-5)sinx ]
=lim(x->5-) -x/[(x-1)sinx ]
= -5/(4sin1)
x=5: 跳跃间断点 (第1类间断点)
ans : C