LINEAR EQUATIONS IN TWO
VARIABLES
A JOURNEY INTO THE WORLD OF LINES
CLASS : 9
PRESENTED BY: AYUSHI NEGI
• DEFINITION: AN EQUATION IS A MATHEMATICAL STATEMENT
THAT SHOWS TWO EXPRESSIONS ARE EQUAL. IT CONTAINS
AN EQUALITY SIGN (=).
• * EXAMPLES:
• *5+3=8
• * X + 7 = 10
WHAT IS • * 2Y = 14
AN
EQUATION?
WHAT IS A LINEAR EQUATION?
• DEFINITION: AN EQUATION IN WHICH THE HIGHEST
POWER OF THE VARIABLE (OR VARIABLES) IS 1.
• * WHY “LINEAR”? BECAUSE WHEN PLOTTED ON A
GRAPH, ITS SOLUTIONS FORM A STRAIGHT LINE.
• * EXAMPLES (LINEAR EQUATION IN ONE VARIABLE):
• * X + 5 = 12
• * 3Y = 9
• *Z–2=5
WHAT IS A LINEAR EQUATION IN TWO VARIABLES?
• AN EQUATION THAT CAN BE WRITTEN IN THE FORM AX + BY + C = 0, WHERE A, B, AND C ARE
REAL NUMBERS, AND A AND B ARE NOT BOTH ZERO.
• * KEY CHARACTERISTICS:
• * TWO VARIABLES (E.G., X AND Y)
• * HIGHEST POWER OF EACH VARIABLE IS 1.
• * EQUALITY SIGN.
* 2X + 3Y = 5
EXAMPLES * 4X – Y = 7
OF LINEAR * X + Y – 10 = 0
EQUATIONS * Y = 2X – 1 (CAN BE REWRITTEN AS 2X - Y - 1 = 0)
IN TWO
VARIABLES
HOW TO FIND SOLUTIONS?
• ASSUME A VALUE FOR ONE VARIABLE AND SOLVE
FOR THE OTHER.
• * EXAMPLE: FOR 2X + Y = 6
• * IF X = 0, 2(0) + Y = 6 \IMPLIES Y = 6.
SOLUTION: (0, 6)
• * IF Y = 0, 2X + 0 = 6 \IMPLIES X = 3.
SOLUTION: (3, 0)
SOLUTIONS OF A LINEAR EQUATION IN TWO
VARIABLES
• A PAIR OF VALUES (X, Y) THAT SATISFIES THE EQUATION (I.E., MAKES THE EQUATION TRUE
WHEN SUBSTITUTED).
• * IMPORTANT NOTE: A LINEAR EQUATION IN TWO VARIABLES HAS INFINITELY MANY
SOLUTIONS.[WHY? BECAUSE A LINE CONSISTS OF INFINITELY MANY POINTS. EACH POINT ON
THE LINE REPRESENTS A SOLUTION.]
• * A LINEAR EQUATION IN TWO VARIABLES IS OF THE FORM
AX + BY + C = 0.
• * IT HAS INFINITELY MANY SOLUTIONS.
• * EACH SOLUTION IS AN ORDERED PAIR (X, Y).
• * ITS GRAPH IS ALWAYS A STRAIGHT LINE.
• * WE CAN FIND SOLUTIONS BY SUBSTITUTING VALUES AND
CAN GRAPH THEM TO VISUALIZE THE RELATIONSHIP.
SUMMARY
“THANK YOU FOR
YOUR
ATTENTION!