这题是sin^2(x+1)/(x-1)?,sin^2(x+1)当x趋于1不就等于sin^2 2
分母趋于0所以极限无穷大.
如果是sin^2(x-1)/(x-1)那么由等价无穷小,= (x-1)^2 / (x-1) = 0