Other simple Javascript exercises

My simple Javascript exercises colection starts from page: Some simple Javascript exercises. In this article I propose more.

Exercise 4
Solve a second order equation

`<!DOCTYPE html><html><head><script>function equation2degree() {  var a = document.getElementById("number1").value;  a=parseFloat(a);  var b = document.getElementById("number2").value;  b=parseFloat(b);  var c = document.getElementById("number3").value;  c=parseFloat(c);  var delta = b*b-(4*a*c);  if (delta < 0)  {     document.getElementById("solution").innerHTML = "Impossible";  }  else  {     var x1=(-b+Math.sqrt(delta))/(2*a);     var x2=(-b-Math.sqrt(delta))/(2*a);               document.getElementById("solution").innerHTML = "x<sub>1</sub>=" + x1 + "&nbsp;&nbsp;x<sub>2</sub>=" + x2;  }}</script></head><body>  <h3>Solve a second order equation in the form ax<sup>2</sup>+bx+c=0</h3>  <p>Insert the coefficients (integer or real numbers, with negative sign if present)<BR><BR>  a: <input type="text" id="number1"><BR><BR>  b: <input type="text" id="number2"><BR><BR>  c: <input type="text" id="number3"><BR><BR>  <button onclick="equation2degree()">Solve!</button></p>  <p>Solution:&nbsp;&nbsp;<span id="solution"></span></p></body></html>`

Exercise 5

Determine if a year is a leap year.
All years whose number represents them is a multiple of 4, are leap years, except for secular years (ie multiples of 100) if their number is not a multiple of 400.

`<!DOCTYPE html><html><head><script>function leapYear() {  var year = parseInt(document.getElementById("year").value);  var leap = false;  if (year%100==0)   // is it a secular year?  {    if (year%400==0)    {      leap = true;    }  }  else   // all other years!  {    if (year%4==0)    {      leap = true;    }  }  ``document.getElementById("print").innerHTML = leap;}</script></head><body>  <h3>Tell me a year and I determine if it is a leap year!</h3>  Gimme the year: <input type="number" id="year">  <button onclick="leapYear()">Submit</button>  <BR><p>Answer: <span  id="print"></span></p><BR></body></html>`