var i = 0;
function fact()
{
document.getElementById("base").innerHTML="<div id='description'><h1>Factorial solver</h1>Enter n in this form:<br><br><img src='factorial.png' width='28' height='30' alt='factorial'></div><div><form name='factorial'>n:<input type='text' name='n' size='6' ><br><br><input type='button' value='Solve' onClick='factsolve()'><br><br></form>Solution: </div><div id='answers'></div><br>";
i = 1;
document.getElementById("trigonometry").src="trigonometry_off.png";
document.getElementById("factorial").src="factorial_selected.png";
document.getElementById("quadric_equation").src="quadric_equation_off.png";
}
function quad()
{
document.getElementById("base").innerHTML="<h1> quadric equation solver</h1>Enter a , b and c in this form:<br><br><img src='quadric_equation.png' width='202' height='35' alt='quadric equation'></div><div style='white-space:pre;'><form name='quadraticEquation'>A:<input type='text' name='a' size='6'> B:<input type='text' name='b' size='6' > C:<input type='text' name='c' size='6' ><br><br><input type='button'  value='Solve' onClick='quadsolve()'><br><br></form>Solution:</div><div id='answers'> </div><br></div>";
i = 2;
document.getElementById("trigonometry").src="trigonometry_off.png";
document.getElementById("quadric_equation").src="quadric_equation_selected.png";
document.getElementById("factorial").src="factorial_off.png";
}
function trig()
{
document.getElementById("base").innerHTML="<h1> Trigonometric functions solver</h1>To get sin(n), cos(n), tan(n) Enter n in degrees in this form:<br><br><img src='trigonometry.png' alt='trigonometry function'></div><div><form name='trigonometry'>n:<input type='text' name='num' size='6'><br><br><input type='button' value='Solve' onClick='trigsolve()'><br><br><img src='arctrigonometry.png' ><br><br>n:<input type='text' name='arcnum' size='6'><br><br><input type='button' value='Solve' onClick='arctrigsolve()'></form>Solution:</div><div id='answers'> </div><br></div>";
i = 3;
document.getElementById("trigonometry").src="trigonometry_selected.png";
document.getElementById("factorial").src="factorial_off.png";
document.getElementById("quadric_equation").src="quadric_equation_off.png";
}
/**********************************************************************************************************************************/
function quadon()
{
	if(i != 2)
		document.getElementById("quadric_equation").src="quadric_equation_on.png";
}
function quadoff()
{
	if(i != 2)
		document.getElementById("quadric_equation").src="quadric_equation_off.png";
}
function facton()
{
	if(i != 1)
		document.getElementById("factorial").src="factorial_on.png";
}
function factoff()
{
	if(i != 1)
		document.getElementById("factorial").src="factorial_off.png";
}
function trigon()
{
	if(i != 3)
		document.getElementById("trigonometry").src="trigonometry_on.png";
}
function trigoff()
{
	if(i != 3)
		document.getElementById("trigonometry").src="trigonometry_off.png";
}
/**********************************************************************************************************************************/
function quadsolve()
{
		var a, b, c, d;
		a = document.quadraticEquation.a.value;
		b = document.quadraticEquation.b.value;
		c = document.quadraticEquation.c.value;
		if(a != 0)
		{
			d = Math.pow(b,2) - 4*a*c;
			if(d < 0)
					document.getElementById("answers").innerHTML="There is no real solution to the equation.";
			else
				if(d == 0)
					document.getElementById("answers").innerHTML="x = " + (-b/(2*a));
				else
				{
					document.getElementById("answers").innerHTML="x<span id='small'>1</span> = " + ((-b+Math.sqrt(d))/(2*a)) + "<br>" +
					"x<span id='small'>2</span> = " + ((-b-Math.sqrt(d))/(2*a));		
				}
		}
		else
				document.getElementById("answers").innerHTML="The equation is not a quadratic equation.";	
}
function factsolve()
{
	var sum = 1 , factorial = document.factorial.n.value;
	for (i = 1 ; i <= factorial ; i++)
	{
		sum*=i;
	}
	if(factorial == 0)
		sum = 1;
	document.getElementById("answers").innerHTML="n= " + sum;
}
function trigsolve()
{
	var s, c, t, num, numrad;
	num = document.trigonometry.num.value;
	numrad = num*Math.PI/180;
	s = Math.sin(numrad);
	c = Math.cos(numrad);
	t = Math.tan(numrad);
	document.getElementById("answers").innerHTML="sin(" + num + ") = " + s + "<br>cos(" + num + ") = " + c + "<br>tan(" + num + ") = " + t;
}
function arctrigsolve()
{
	var  arcs, arcc, arct, arcnum;
	arcnum = document.trigonometry.arcnum.value;
	arcs = Math.asin(arcnum)*180/Math.PI; 
	arcc = Math.acos(arcnum)*180/Math.PI;
	arct = Math.atan(arcnum)*180/Math.PI;
	document.getElementById("answers").innerHTML="arcsin(" + arcnum + ") = " + arcs + "<br>arccos(" + arcnum + ") = " + arcc + "<br>arctan(" + arcnum + ") = " + arct;
}