-1、 equation ax^2+bx+c=0, The root of quadratic equation of one variable .

Explain :

<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title> Untitled Document </title>
</head>

<body>
<input type="number" id="n1" placeholder=" Input a value "/>
<input type="number" id="n2" placeholder=" Input b value "/>
<input type="number" id="n3" placeholder=" Input c value "/>
<input type="button" value=" Confirm the function value " onclick="ABC()" />      //onclick Reference function ABC
</body>
</html>
<script>
function ABC()                                                                      // Set function
{
var a=document.getElementById("n1").value
var b=document.getElementById("n2").value
var c=document.getElementById("n3").value
if(a!=""&&b!=""&&c!="")
{
var d=(b*b-4*a*c)
if(a!=0)
{
if(d>0)
{
alert(" There are two roots "+(-b+Math.sqrt(d))/(2*a)+" and "+(-b-Math.sqrt(d))/(2*a))
}
else
{
if(d==0)
{
alert(" There is a real root for "+(-b)/(2*a))
}
else
{
alert(" No real roots ")
}
}
}

else
{
alert(" It's not a quadratic equation of two variables , There is a root for "+(-c)/b)
}

}
else
{
alert(" Please enter a number ")
}
}
</script>


2、 Enter year 、 month 、 And output the date format

<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>year、month、day</title>
</head>

<body>
</body>
</html>
<script>
var year=prompt(" Please enter the year ")
if(year!=null)                       // Press the OK button
{
var number=isNaN(year)      // Judge year Is it a numerical value , It's the number. false, Not numbers true
if(number==false)
{
if(year>0&&year<=9999&&year%1==0)
{
var month=prompt(" Please enter the month ")
if(month!=null)
{
var number1=isNaN(month)
if(number1==false)
{
if(month>0&&month<=12&&month%1==0)
{
var day=prompt(" Please enter the date ")
if(day!=null)
{
var number2=isNaN(day)
if(number2==false)
{
if(day>0&&day<=31&&day%1==0)
{
if(month==1||month==3||month==5||month==7||month==8||month==10||month==12)
{
alert(year+" year "+month+" month "+day+" Japan ")
}
else if(month==4||month==6||month==9||month==11)
{
if(day>0&&day<=30)
{
alert(year+" year "+month+" month "+day+" Japan ")
}
else
{
alert(" Wrong input date ")
}
}
else if(month==2)
{
if(year%4==0&&year%100!=0||yeas%400==0)
{
if(day>0&&day<=29)
{
alert(year+" year "+month+" month "+day+" Japan ")
}
else
{
alert(" Wrong input date ")
}
}
else
{
if(day>0&&day<=28)

{
alert(year+" year "+month+" month "+day+" Japan ")
}
else
{
alert(" Incorrect input ")
}
}
}
}
else
{
alert(" You have not entered a valid date ")
}
}
else
{
alert(" The date you entered is wrong ")
}
}
}
else
{
alert(" You have not entered a valid month ")
}
}
else
{
alert(" The month you entered is wrong ")
}
}
}
else
{
alert(" You have not entered the correct year ")
}
}
else
{
alert(" Incorrect input ")
}
}
</script>


3、 Do you run faster than a leopard ?

<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title> Untitled Document </title>
</head>

<body>
Can you run past a leopard <input type="text" id="use" placeholder=" Can you run past a leopard " />
<input type="button" value=" Click ok " onclick="a()" />
</body>
</html>
<script>
function a()
{
var on=document.getElementById("use").value;
if(on==" can ")
{
alert(" You are more than a beast ")
}
else
{
if(on==" You can't ")
{
alert(" Even animals are inferior to ")
}
else
{
alert(" Please input whether you can live or not ")
}
}
}
</script>

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