function suvat(v,i){
  if(i==0)return showterms([[1,v]]);
  switch(v){
case "s": return "the distance travelled";
case "u": return "the initial velocity";
case "v": return "the final velocity";
case "a": return "the acceleration";
case "t": return "the time of travel";
}};


var equns=new Array(5);
equns["s"]=showterms([[1,'v']," = ",[1,'u'],[1,Var('a t')]]);
equns["a"]=onelinemid(showterms([[1,'s']," = "]),Frac(showterms([[1,'u'],[1,'v']]),showNB(2)),
  showterms([[1,'t']]));
equns["v"]=onelinemid(showterms([[1,'s']," = ",[1,Var('u t')]," + "]),Frac(1,2,"polysmall"),
  showterms([[1,Var('a t'),2]]));
equns['t']=showterms([[1,'v',2]," = ",[1,'u',2],[2,Var('a s')]]);
equns["u"]=onelinemid(showterms([[1,'s']," = ",[1,Var('v t')],minusch2]),Frac(1,2,"polysmall"),
  showterms([[1,Var('a t'),2]]));


function units(x,desc){//alert("eval "+x+"="+eval(x));
  if(arguments.length==1)desc=descp;
  var vl=eval(x);
	switch(x){
	case "s":return desc==0?showterms([[' m',1]],"polysmall"):" metre"+(vl==1?"":"s");
	case "u":case "v":return (desc==0?showterms([[' ms',1,-1]],"polysmall"):" metre"
	  +(vl==1?"":"s")+" per second");
	case "t":return (desc==0?showterms([[' s',1]],"polysmall"):" second"+(vl==1?"":"s"));
	case "a":return (desc==0?showterms([[' ms',1,-2]],"polysmall"):" metre"+(vl==1?"":"s")
	  +" per second per second");
	}};

function shwevl(s,e){ this.shw=s;this.evl=e };

var A,B,C,solvequad=false,twosolns=false,oneroot=false;

function rearr(missvar,findvar,bef,aft){//alert("mising="+missvar+" find="+findvar);
   if(arguments.length<4)aft="";
   if(arguments.length<3)bef="";
   switch(missvar){
    case "s":switch(findvar){
       case "v":return new shwevl(showterms([[1,'v']," = ",[1,'u'],[1,'a t']]),u+a*t);break;
       case "u":return new shwevl(showterms([[1,'u']," = ",[1,'v'],[-1,Var('a t')]]),
         v-a*t);break;
       case "a":return new shwevl(onelinemid(showterms([[1,'a']," = "]),
            Frac(showterms([[1,'v'],[-1,'u']]),showterms([[1,'t']]))),
            (v-u)/t);break;
       case "t":return new shwevl(onelinemid(showterms([[1,'t']," = "]),
            Frac(showterms([[1,'v'],[-1,'u']]),showterms([[1,'a']]))),
         (v-u)/a);break;
       };break;
    case "a":switch(findvar){
        case "s":return new shwevl(onelinemid(showterms([[1,'s']," = "]),
           Frac(showterms([[1,'u'],[1,'v']]),showNB(2)),
            showterms([[1,'t']])),(u+v)*t/2);break;
        case "t":return new shwevl(onelinemid(showterms([[1,'t']," = "]),
            Frac(showterms([[2,'s']]),showterms([[1,'u'],[1,'v']]))),2*s/(u+v));break;
        case "u":return new shwevl(onelinemid(showterms([[1,'u']," = "]),
               Frac(showterms([[2,'s']]),showterms([[1,'t']])),showterms([[-1,'v']])),
            2*s/t-v);break;
        case "v":return new shwevl(onelinemid(showterms([[1,'v']," = "]),
               Frac(showterms([[2,'s']]),showterms([[1,'t']])),showterms([[-1,'u']])),
             2*s/t-u);break;
        };break;
    case "v":switch(findvar){
        case "s":return new shwevl(onelinemid(showterms([[1,'s']," = ",[1,Var('u t')]," + "]),
             Frac(1,2,"polysmall"),showterms([[1,Var('a t'),2]])),u*t+a*t*t/2);break;
        case "u":return new shwevl(onelinemid(showterms([[1,'u']," = "]),
              Frac(showterms([[1,'s']]),showterms([[1,'t']])),spn(minusch2),
              Frac(1,2,"polysmall"),showterms([[1,Var('a t')]])),
              s/t-a*t/2);break;
        case "a":return new shwevl(onelinemid(showterms([[1,'a']," = "]),
           Frac(showterms([[2,1],"( ",[1,'s'],[-1,Var('u t')]," )"]),
           showterms([[1,'t',2]]))), 2*(s-u*t)/t/t);break;
        case "t": solvequad=true;twosolns=true;A=a/2;B=u;C=-s;
               oneroot=equals(B*B-4*A*C,0);
              return new shwevl(onelinemid(Frac(1,2,"polysmall"),
                   showterms([[1,Var('a t'),2],[1,Var('u t')],[-1,'s']," = ",[0,1]])),
                  [(-B+Math.sqrt(B*B-4*A*C))/2/A,(-B-Math.sqrt(B*B-4*A*C))/2/A]);break;
        };break;
     case "t":switch(findvar){
        case "v":twosolns=!equals(u*u+2*a*s,0);
           return new shwevl(showterms([[1,'v']," = ","&plusmn;&radic;( ",[1,'u',2],
           [2,Var('a s')]," )"]),
           [Math.sqrt(u*u+2*a*s),-Math.sqrt(u*u+2*a*s)]);break;
        case "u":twosolns=!equals(u*u+2*a*s,0);
           return new shwevl(showterms([[1,'u']," = ","&plusmn;&radic;(",[1,'v',2],
           [-2,Var('a s')]," )"]),
           [Math.sqrt(v*v-2*a*s),-Math.sqrt(v*v-2*a*s)]);break;
        case "a":return new shwevl(onelinemid(showterms([[1,'a']," = "]),
            Frac(showterms([[1,'v',2],[-1,'u',2]]),showterms([[2,'s']]))),
            (v*v-u*u)/2/s);break;
        case "s":return new shwevl(onelinemid(showterms([[1,'s']," = "]),
             Frac(showterms([[1,'v',2],[-1,'u',2]]),showterms([[2,'a']]))),
             (v*v-u*u)/2/a);break;
        };break;
     case "u":switch(findvar){
        case "s":return new shwevl(onelinemid(showterms([[1,'s']," = ",[1,Var('v t')],
        minusch2]),Frac(1,2,"polysmall"),
          showterms([[1,Var('a t'),2]])),v*t-a*t*t/2);break;
        case "v":return new shwevl(onelinemid(showterms([[1,'v']," = "]),
             Frac(showterms([[1,'s']]),showterms([[1,'t']])),spn(" + "),
             Frac(showterms([[1,Var('a t')]]),spn(2))
           ),s/t+a*t/2);break;
        case "a":return new shwevl(onelinemid(showterms([[1,'a']," = "]),
            Frac(showterms([[2,1],"( ",[1,Var('v t')],[-1,'s']," )"]),showterms([[1,'t',2]]))),
           2*(v*t-s)/t/t);break;
        case "t":solvequad=true;twosolns=true;A=a/2;B=-v;C=s;
             oneroot=equals(B*B-4*A*C,0);
            return new shwevl(onelinemid(Frac(1,2,"polysmall"),
                showterms([[1,Var('a t'),2],[-1,Var('v t')],[1,'s']," = ",[0,1]])),
               [(-B+Math.sqrt(B*B-4*A*C))/2/A,(-B-Math.sqrt(B*B-4*A*C))/2/A]);break;
        };break;
      }
 };
 
if(args.suvatFind||args.suvatMiss){
   givenf="suvat";
   if(args.suvatFind){findvar=args.suvatFind;
     if("suvat".indexOf(findvar)==-1)halt("suvatFind URL parameter must be 1 of s,u,v,a and t");
    }else{findvar=""};
   givenf=givenf.replace(findvar,"")
   if(args.suvatMiss){missvar=args.suvatMiss;
     if("suvat".indexOf(missvar)==-1)halt("suvatMiss URL parameter must be 1 of s,u,v,a and t");
    }else{missvar=""};
   givenf=givenf.replace(missvar,"");
   if(findvar==""){findvar=randelt(givenf);givenf=givenf.replace(findvar,"")};
   if(missvar==""){missvar=randelt(givenf);givenf=givenf.replace(missvar,"")};
   //alert("find="+findvar+" miss="+missvar);
   // alert(givenf+" find="+findvar+" miss="+missvar);
   givenf=(givenf+findvar+missvar); 
}
else { givenf=newvars(5,"suvat").join("");  
      findvar=givenf.charAt(3);missvar=givenf.charAt(4)
     };
  
//alert("givenf "+givenf+" findvar="+findvar+" missvar="+missvar);

function given(v){return findvar!=v && missvar!=v};

var descp=randint(0,1);

function desc(x,d){if(arguments.length==1)d=descp;
   return suvat(givenf.charAt(x),d) };

function descp1(x){if(descp==0)return desc(x,0)
  else return desc(x,1)+" ("+desc(x,0)+") "};

function val(x,d){if(arguments.length==0)d=descp;
  return (d==0?spn(" = "):" is ")+showterms([[eval(givenf.charAt(x)),1]])
     +units(givenf.charAt(x),d)
};

function showval(x,d){if(arguments.length==1)d=descp; 
return desc(x,d)+val(x,d)
};

function showWorkedsuvatSOLN(){
document.writeln(
 "We need a <i>suvat</i> equation with ",
  desc(0,0),", ",desc(1,0),", ",desc(2,0)," as well as ",
  desc(3,0),"; i.e. an equation with ",desc(4,0)," missing.<br>",
  ("avu".indexOf(missvar)==-1?oneline:onelinemid)
    ("So the  equation to use is:",equns[missvar]),
  (' vss s'.charAt(1+"savtu".indexOf(missvar))!=findvar
    ?"Rearranging to find "+desc(3,0)+(solvequad?" we get the quadratic equation:":"")+"<blockquote>"+
      SOLN.shw+"</blockquote>"
    :""
  ),
    "Substituting the values given for the variables we  ",
    (solvequad?" can solve "+showterms([[A,Var(findvar),2],[B,Var(findvar)],[C,1]," = ",[0,1]])
        +" to find "+(oneroot?"two equal":"two")+" real roots:<br>"
    :twosolns
    ? " have "+showterms([[1,findvar]," = ",[dps(SOLN.evl[0],3),1]])+" or "+showterms([[dps(SOLN.evl[1],3),1]])
    : " have "+showterms([[1,findvar]," = ",[dps(SOLN.evl,3,'s'),1]])
    ),
    (twosolns?(oneroot?showterms([[1,findvar]," = ",[dps(SOLN.evl[0],3,'s'),1]])
     :"<br>Either of the two values is correct: "+showterms([[dps(SOLN.evl[0],3),1]])+" and "+
      showterms([[dps(SOLN.evl[1],3),1]])
      ):""),
    units(findvar,0), " to 3 dps."

   );
};