p=solve('a*x^2+b*x+c=0')             % solve( )：解方程，變量缺省時(shí)，系統(tǒng)默認(rèn)為x 
p =
[ 1/2/a*(-b+(b^2-4*a*c)^(1/2))]             %  
[ 1/2/a*(-b-(b^2-4*a*c)^(1/2))]             %