f(1)=2/3
limf(x)左=2/3
limf(x)在x從右邊趨于1時(shí)其值用f(x)=x^2計(jì)算,為1,顯然不等于此點(diǎn)的函數(shù)值,所以就不存在,
從圖形上看,在x=1時(shí)曲線也不連續(xù),