## Standard form of equation

The equations are named based on the degree of the equations.

The equations with degree 1 are known as linear equations.

The equations of degree 2 are known as quadratic equations.

The equations of degree 3 are known as cubic equations and so on.

### Standard form of linear equation

The standard form of a linear equation is given by Ax+ By = C where A, B and C are constants and x and y are variables

Example: -

Find the equation of the line passing through (6, -2) and having a slope 3.

Solution: -

We know that if a line passes through a point (x

_{1}, y

_{1}) and have slope m, then the equation is given by y - y

_{1}= m (x - x

_{1}). This form is known as point slope form.

Given that the line passing through (6, -2). That is (x

_{1}, y

_{1}) = (6, -2).

Slope is 3. That is m = 3

Therefore the required line is

y - (-2) = 3 (x - 6)

y + 2 = 3x - 18

adding 18 both sides, we get

y + 20 = 3x

subtracting y on both sides, we get

**3x - y = 20, which is the required equation.**

### Standard form of quadratic equation

The standard form of the quadratic equation is ax

^{2}+ bx + c = 0, a ≠ 0.

**Example: -**

Write the quadratic equation in standard form.

2x

^{2}= 12x + 3

**Solution: -**

We know that the standard form of the quadratic equation is given by ax

^{2}+ bx + c = 0, a ≠ 0.

Given equation is 2x

^{2}= 12x + 3

To convert this to standard form, we take all terms to left.

Subtracting 12x and 3 on both sides, we get

**2x**

^{2}- 12x - 3 = 0, which is the required standard form## Standard form of conic sections

A

*is defined as the locus of a point which moves in a plane so that its distance from a fixed point in the plane bears a constant ratio to its distance from a fixed line in the plane. The fixed point is called*

**conic section or conic***, the fixed line is called the*

**focus***, and the constant ratio is called*

**directrix***of the conic. The eccentricity of a conic is denoted by*

**eccentricity**

**e**

### Standard form of a parabola

*The standard form of a parabola is given by*

**y = ax**. It is the general quadratic equation.

^{2}+ bx + c, a ≠ 0If a > 0, the parabola opens upwards and if a < 0, the parabola opens downwards.

Example: -

Write the equation of the parabola whose focus is S(-4,5) and vertex (-4,1).

Solution: -

Distance between the focus and the vertex = 4

Distance between the vertex and the directrix = 4

Distance between the vertex and x axis = 1

Therefore distance between x axis and directrix =3

Since the directrix is parallel to x axis and at a distance of 3 units below the x axis, the equation to the directrix is y = -3

Let P(x,y) be any point on the parabola. Let PM be the perpendicular to the directrix.

Then SP

^{2}= (x + 4)

^{2}+ (y - 5)

^{2}PM

^{2}= (y + 3)

^{2}

Since SP

^{2}= PM

^{2}, we get

(x + 4)

^{2}+ (y - 5)

^{2}= (y + 3)

^{2}

Simplifying we get

x

^{2}+ 8x + 16 + y

^{2}- 10y + 25 = y

^{2}+ 6y + 9

Cancelling common terms, we get

x

^{2}+ 8x + 16 - 10y + 25 = 6y + 9

subtracting 6y and 9 on both sides, we get

x

^{2}+ 8x -16y +32 =0

Write all terms in x and constants on one side

16y = x

^{2}+ 8x + 32

Dividing by 16 on both sides, we get

**y = x**

^{2}/16 + 1/2x + 2, is the required equation of the parabola.### Standard form of a circle

*I*

*f th*e center of the circle is at the point (h, k) and has radius of the circle is r, then the equation of the circle is given by

**(x - h)**

^{2}+ (y - k)^{2}= r^{2}.**Example: -**

Write the equation of the circle in the standard form, whose center is (6, 9) and radius is 2.

**Solution: -**

Given center of the circle,(h, k) = (6, 9) and radius of the circle, r = 2.

We know that the standard form of a circle is (x - h)

^{2}+ (y - k)

^{2}= r

^{2}

Substituting for h, k and r, we get

(x - 6)

^{2}+ (y - 9)

^{2}= 2

^{2}

Simplifying we get,

(x - 6)

^{2}+ (y - 9)

^{2}= 4

**So the required equation is (x - 6)**

^{2}+ (y - 9)^{2 }= 4.## Standard form of numbers

^{y},where x is a decimal number with only one number before decimal.

**Example: -**

Write the number 47956.759 in the standard form.

**Solution: -**

Given number is 47956.759. we have to write this number in standard form.

In the standard form we write the number in the form x * 10

^{y},where x is a decimal number with only one number before decimal.

That is 47956.759 = 4.7956759 x 10

^{4}

**So the standard form of 47956.759 = 4.7956759 x 10**

^{4}## Converting standard form

### Converting parabola from standard from to vertex form

- First we have to take the common factors from the first two terms in the standard form f(x) = ax
^{2}+ bx + c - Now we complete the square of the first two terms by adding and subtracting square of the half of second term.
- Simplify and rearrange it in the form y = a(x - h)
^{2}+ k

Example: -

Convert the parabola f(x) = x^{2} - 6x + 6 in the standard form to vertex form and hence find the vertex.

Solution: -

Given standard form of parabola is f(x) = x^{2} - 6x + 6.

Comparing with the standard form of parabola, f(x) = ax^{2} + bx + c, we get

a = 1.

Since
a = 1, we complete the square of the first two terms in the quadratic
equation. To complete the square, we add and subtract the square of the
half of the second term.

So we get

f(x) = x^{2} - 6x + 9 - 9 + 6

Now we can combine the first three terms and last two term.

We get,**f(x) = (x - 3) ^{2} - 3, which is the required vertex form and the vertex is given by (3, -3).**

**Converting slope intercept form to standard form**

When we take all the variables to one side and keep the constants on the other side, we get the standard form.

**Example: -**

Convert the line y = 5x + 8 into standard form.**Solution: -**

Given
line is y = 5x + 8. To convert into standard form, we have to take all
variables to one side, keeping the constants on the other side.

For this lets subtract 5x from both sides,

y = 5x + 8__-5x -5x __

y - 5x = 8**So the required equation is -5x + y = 8**

## Functions in standard form

### Standard form of a quadratic function

The standard form of a quadratic function is given by

f(x) = a(x - h)

^{2}+ k, where a ≠ 0.

This form is also known as vertex form of a quadratic function

### Standard form of a polynomial function

When we arrange the polynomial in the decreasing order of its degree, it is said to be in the standard form. In general, an nth degree polynomial P(x) = a

_{n}x

^{n}+ a

_{n-1}x

^{n-1}+ ...+ a

_{1}x + a

_{0}where a

_{n}, a

_{n-1},... are constants and a

_{n}≠ 0 is in the standard form. Here we can see that the power of x in each term decreases.