I need help. A homework problem superimposes a graph atop a DE. What am I doing wrong: _____________ plot1 := phaseportrait(eqn,y(x), x=-0.25..0.25, [[y(-1/2)=2],[y(3/2)=0]],titlefont=[TIMES,ROMAN,18],title=`Sec 2.1 #17`, color=grey, linecolor=[red,blue]): plot2 := (1/2)*x^2: display([plot1,plot2]); Error, (in DEtools/phaseportrait) the 'number' option must be specified before initial conditions Error, (in plots:-display) expecting plot structures but received: [plot1, (1/2)*x^2] _____________