# Equation

In this mini-lesson, we will explore the concept of equationsÂ by knowing the definition of an equation, equation examples, equation of a circle, quadratic equation, linear equation, and types of equations.

Before we get started, let's see what Joe did.

Joe createdÂ a game called 'Mind Reader.'

He wants to playÂ it with his friends.

He asks one of his friends, Kaira, to think of a number, multiply it by 2, and subtract 5 from it.

He asks herÂ the final result.

Kaira says, 'It is 13.'

Joe instantly says that the number Kaira thought of initially was 9

Kaira nods and Joe's friendsÂ including Kaira areÂ surprised!

Everybody wants to know how the game 'Mind Reader'Â works.

Do you knowÂ how it works?

By the end of this short lesson, you will understandÂ how it works.

## What areÂ Equations?

### Meaning of Equation in Maths

An equation is a mathematical statement with an 'equal to'Â symbol between two algebraic expressions that have equal values.

For example, $$2x+9$$ is the expression on the left-hand side that is equated with the expression 24 on the right-hand side.

Look at the following examples. These will give you an idea of the meaning of an equation in math.

Â  Equations Is it an equation?
1. $$y=8x-9$$ Yes
2. $$y+x^2-7$$ No, because there is no 'equal to' symbol.
3. $$7+2=10-1$$ Yes

## How Do You Solve Equations?

An equation is like a weighing balance with equal weights on both sides.

If we add or subtract the same number from both sides of an equation, it still holds.

Similarly, if we multiply or divide the same number on both sides of an equation, it still holds.

Consider the equation of a line, $$3x-2=4$$

We will perform mathematical operations on theÂ LHS and the RHS so that the balance is not disturbed.

Let's add 2 on both sides to reduce the LHS to $$3x$$

This will not disturb the balance.

The new LHS is $$3x-2+2=3x$$ and the new RHS is $$4+2=6$$

Now, let's divide both sides by 3 to reduce the LHS to $$x$$

Thus, the solution of the equation of a line is $$x=2$$

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Think Tank
1. Solve the following riddle.

## What Are the 3 Types of Equations?

There are 3 main types of equations in math.

### Linear Equation

The standard form of a linear equation withÂ variables $$x$$ and $$y$$Â is:

 $$Ax+By=C$$

The standard form of a quadratic equation withÂ variableÂ $$x$$ is:
 $$ax^2+bx+c=0$$, where $$a\neq 0$$

### Cubic Equation

The standard form of a cubic equation withÂ variableÂ $$x$$ is:Â

 $$ax^3+bx^2+cx+d=0$$, where $$a\neq 0$$

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Important Notes
1. The values of the variable that makes an equation true are called the solution or root of the equation.
2. The solution of an equation is unaffected if the same number is added, subtracted, multiplied, or divided on both sides of the equation.
3. The graph of a linear equationÂ in one or two variables is a straight line.
4. The curve of the quadratic equation is in the form of a parabola.

## Equation Calculator

Try solving linear equations in one variable using the equation calculatorÂ below.

## Solved Examples

 Example 1

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Hailey loves to collectÂ pennies and dimesÂ in her piggy bank.

She knows that the total sumÂ in her piggy bank is Rs.100Â and it has 3 times as many coins of Rs.5 as notes of Rs.10 in it.

She wants to know the exact number of coins of Rs.5 and the number of notes ofÂ Rs.10 in her piggy bank.Â

Can you help her find the count?

Solution

Let the number ofÂ notes of Rs.10 be $$x$$.

Then the number ofÂ coins of Rs.5 will be $$3x$$

Therefore, total amount = $$(10\times x)+(5Â \times 3x)=10x+15x=25x$$

According to the information we have,

\begin{align}25x&=100\\[0.2cm]x&=4\end{align}

Therefore,Â

 The number of notes of Rs.10 is, $$x=4$$ The number of cois of Rs.5 is, $$3x=12$$
 Â  Â Example 2

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Mia is a fitness enthusiast who goes running every morning.

The park where she jogs is rectangular in shape and measures $$12\;\text{metres}$$ by $$8\;\text{metres}$$.

An environmentalist group plans to revamp the park and decides to build a pathway surrounding the park.

This would increase the total area to $$140\;\text{sq. metres.}$$

What will be the width of the pathway?

Solution

Letâ€™s denote the width of the pathway as $$x$$.

Then, the length and breadth of the outer rectangle is $$(12+2x)\;\text{metres }$$Â and $$(8+2x)\;\text{metres}$$

According to the question,
\begin{align}(12+2x)(8+2x)&=140\\2(6+x)\cdot 2(4+x)&=140\x+6)(x+4)&=35\\x^2+10x-11&=0\\x^2+11x-x-11&=0\\x(x+11)-(x+11)&=0\\(x+11)(x-1)&=0\\x&=1,-11\end{align} SinceÂ length canâ€™t be negative, we take \(x=1

 $$\therefore$$ Width of the pathwayÂ  $$= 1\;\text{metre}$$
 Example 3

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Meghan will begin attending classes for theÂ sixth grade from next week.

He suddenly realized thatÂ he doesn't have either a notebook or a pen.

He goes to a shop to purchase themÂ and realizesÂ that the cost of a notebook is Rs.5 more than twice the cost of the notebook.

Represent this above information usingÂ equations in two variables.

Solution

Let's assume the following.

The cost of aÂ pen = Rs.$$x$$

The cost of a notebook = Rs.$$y$$

According to the given information,

 $$\therefore$$Â $$y = 2x + 5$$

## Interactive Questions on

Here are a few activities for you to practice.

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## Let's Summarize

The mini-lesson targetedÂ the fascinating concept of the equation. The math journey around equation starts with what a student already knows, and goes on to creatively crafting a fresh concept in the young minds. Done in a way that not only it is relatable and easy to grasp, but also will stay with them forever. Here lies the magic with Cuemath.

AtÂ Cuemath, our team of math experts is dedicated to making learning fun for our favorite readers, the students!

Through an interactive and engaging learning-teaching-learning approach, the teachers explore all angles of a topic.

Be it worksheets, online classes, doubt sessions, or any other form of relation, itâ€™s the logical thinking and smart learning approach that we, at Cuemath, believe in.

## 1. What is a true equation?

If the values on both sides of the 'equal to'Â symbol holdÂ true, then the equation is a true equation.

## 2. What is the equation of a circle?

The equation of a circle with radius $$r$$ and center $$(x_{1}, y_{1})$$ is $$(x-x_{1})^2+(y-y_{1})^2=r^2$$.

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