y^( 2/3)+x^(2 /3)=a^(2/3)2/3y ^( -1/3)*y'+(2/3)x^(-1/3)=0y'=- x^( -1/3)/y^(-1/3)在x=0y^( 2/3)=a^(2/3)y=ay'=0切线斜率为0切线y=a
