Chapter 3: Pair of Linear Equations in Two Variables (दो चर वाले रैखिक समीकरण युग्म)
1. Introduction – परिचय
English: In daily life, many situations involve two unknown quantities which are related by two conditions. Such situations are represented mathematically using a pair of linear equations in two variables. हिंदी: वास्तविक जीवन में कई समस्याएँ ऐसी होती हैं जिनमें दो अज्ञात राशियाँ होती हैं और उनके बीच दो शर्तें दी जाती हैं। ऐसी समस्याओं को दो चर वाले रैखिक समीकरणों के युग्म द्वारा व्यक्त किया जाता है।
2. Pair of Linear Equations in Two Variables (दो चर वाले रैखिक समीकरण युग्म)
General Form: a₁x + b₁y + c₁ = 0 a₂x + b₂y + c₂ = 0 Where x and y are variables and a₁, b₁, c₁, a₂, b₂, c₂ are real numbers.
3. Graphical Method of Solution (आलेखीय विधि)
Each linear equation represents a straight line on a graph. The solution of the given pair of equations is the point where both lines intersect.
| Position of Lines | Nature of Solution |
|---|---|
| Intersecting Lines | One Unique Solution |
| Coincident Lines | Infinitely Many Solutions |
| Parallel Lines | No Solution |
4. Algebraic Methods of Solution (बीजीय विधियाँ)
- Substitution Method – प्रतिस्थापन विधि
- Elimination Method – उन्मूलन विधि
- Cross-Multiplication Method – क्रॉस-गुणन विधि
5. Substitution Method (प्रतिस्थापन विधि)
Steps:
- Express one variable in terms of the other.
- Substitute it in the second equation.
- Find the value of one variable.
- Substitute back to find the other variable.
हिंदी: एक समीकरण से एक चर का मान निकालकर दूसरे समीकरण में रखने की विधि को प्रतिस्थापन विधि कहते हैं।
6. Elimination Method (उन्मूलन विधि)
Steps:
- Make coefficients of one variable equal.
- Add or subtract the equations.
- Solve for one variable.
- Substitute to get the other variable.
7. Cross-Multiplication Method (क्रॉस-गुणन विधि)
For equations: a₁x + b₁y + c₁ = 0 a₂x + b₂y + c₂ = 0 Formula: x / (b₁c₂ − b₂c₁) = y / (a₂c₁ − a₁c₂) = 1 / (a₁b₂ − a₂b₁)
8. Consistency of a Pair of Linear Equations (संगतता)
A pair of linear equations is said to be consistent if it has at least one solution. यदि समीकरणों का युग्म कम-से-कम एक हल देता है, तो वह संगत कहलाता है।
9. Consistent Pair (संगत समीकरण युग्म)
- Unique solution (Intersecting lines)
- Infinite solutions (Coincident lines)
10. Inconsistent Pair (असंगत समीकरण युग्म)
A pair of linear equations having no solution is called an inconsistent pair.
11. Conditions for Consistency of Linear Equations (संगतता की शर्तें)
| Condition | Nature of Solution |
|---|---|
| a₁/a₂ ≠ b₁/b₂ | One Unique Solution |
| a₁/a₂ = b₁/b₂ ≠ c₁/c₂ | No Solution |
| a₁/a₂ = b₁/b₂ = c₁/c₂ | Infinite Solutions |
12. Reducible to a Pair of Linear Equations (रैखिक समीकरणों में बदलने योग्य)
Some equations are not linear initially but can be converted into linear equations by suitable substitution. Example: 1/x + 1/y = 4
13. Word Problems based on Linear Equations (कथनात्मक प्रश्न)
Steps to Solve:
- Read the question carefully.
- Assume variables.
- Form linear equations.
- Solve using a suitable method.
- Write the final answer with units.