What is a Linear Equation?

An equation is when two algebraic expressions are equated to each other using an equal “=” sign. An equation with a degree equal to one (the highest power of the variable in the equation is one) is termed a Linear Equation.

What is a Linear Equation in One Variable?

The equations having degree one and a single variable are called a linear equation in one variable.

For example:

4x=12

19x + 45 = 68

What is a Linear Equation in Two Variables?

The equations having degree one and two variables are called a linear equation in two variables.

For example:

3x + 5y = 15

18x = 17 – 2y

Representation of Linear Equations

The linear equation in two variables can be represented graphically. The (x, y) points on the graph are the solution set for the equation which makes the expressions match on both sides of the equal “=” sign.

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This is the graphical representation of a linear equation ax + by + c = 0. Here,

•  a and b are coefficients.

•  x and y are variables.

•  c is a constant term.

Applications of Linear Equations

There are various real-life examples of linear equations. These real-life problems are converted into mathematical forms to form linear equations which are then solved using various methods. It should clearly explain the relationship between the data and the unknowns (variables) in the situation. Below mentioned are the steps to be taken while converting a real-life problem into a linear equation:

• writing the word problem as a mathematical statement in the form of an algebraic expression.

• The quantities whose value can keep changing with time and different inputs are said to be variable quantities. These should be identified and assigned as variables.

• The information given in the problem should be translated and written in a sequential manner.

• After that, equations need to be framed with algebraic expressions and data cited in the word problems.

• These linear equations can then be solved to find out the value of the unknown variables using various methods of equation solving.

• The solutions should be retraced and verified for their correctness and to ensure that they meet all the criteria mentioned in the problem

Some Common Applications of Linear Equations in Real Life Involve Calculations of:

• Age problems

• Speed, time and distance problems

• Geometry problems

• Money and percentage of problems

• Wages and hourly rate problems

• Force and pressure problems 

Solved Examples:

1) The Sum of Two Numbers is 60. One Number is Twice another Number. Find the Numbers.

Solution:

         Let the two numbers be x and y.

         According to the question, the sum of both numbers is 60.

         Therefore, x + y = 60 ————————– (1)

           Now, one number is twice the other number,

         Considering y as the bigger number we can write 2x=y ————————– (2)

         We will now use the substitution method of solving the solutions. Substituting y =       

2x from (2) into (1) we get,

         x + 2x = 60

so, 3x = 60

         x = 60/3

         x = 20

now since y = 2x

         the value of y is 20 x 2 = 40

           y = 40

verifying, x + y = 60

         20 + 40 = 60

Since, LHS = RHS out solution is correct.

Answer) Therefore, the Two Numbers are 20 and 60.

2) If a car travels from city A to city B in 4 hours and covers a distance of 600 kms, find the speed of the car.

Solution:

Let the speed of the car be “S”, time be “t”, and distance be “d”.

We are aware of the relationship between speed, distance and time.

Speed = distance/time

S = d / t

Here d = 600, t = 4.

So, our equation becomes,

S = 600/4

S = 150

Hence, the speed of the car is 150 km/hr. 

3) A daughter is one-fourth her father’s age at present. If after 5 years, the daughter becomes one-third of her father’s age. Then, calculate their present ages.

Solution:

         Let us take x and y as the present ages of the father and daughter.

         Now, at present daughter is one fourth her father’s age

         So, y = x/4 or x= 4y ————————-(1)

         After 5 years, so we add 5 to the present ages.

         (y + 5) = 1/3 (x + 5)

         Or, 3y + 15 = x + 5 ————————-(2)

         Substituting x = 4y from equation (1) to equation (2) we get,

         3y + 15 = 4y + 5

         4y – 3y = 15 – 5

         Hence, y = 10

         Now, x = 4y

         So, x = 4 x 10 = 40.

         Hence, x = 40.

Hence the present age of the father is 40, and that of the daughter is 10.

Do you know

1. Linear Equations were invented by the famous Irish mathematician, Sir William Rowan Hamilton in the year 1843.

2. Linear algebra enjoys a close relationship with linear equations. Linear algebra highlights linear equations and the relationship between variables.