Homeclass 10MathsPair of Linear Equations in Two VariablesCoincident Lines

Coincident Lines

Coincident lines are two or more lines that lie exactly on top of each other on a graph, representing the exact same set of points. In the context of a pair of linear equations in two variables, they occur when one equation is a scalar multiple of the other, resulting in infinitely many solutions.

Key Concepts

Graphically, coincident lines overlap completely on the Cartesian plane, appearing as a single straight line.

Algebraically, a pair of linear equations represents coincident lines when the ratios of their corresponding x-coefficients, y-coefficients, and constant terms are all equal.

This type of linear system is classified as consistent and dependent because every point on the line is a valid solution for both equations.

Formula & Equation

a1/a2 = b1/b2 = c1/c2

a1, b1, c1 are the coefficients and constant of the first equation (a1x + b1y + c1 = 0), and a2, b2, c2 belong to the second equation (a2x + b2y + c2 = 0).

Common Misconceptions

Myth: If two linear equations look different, they cannot represent coincident lines.

Fact: Equations can look different but still be coincident if one is a multiple of the other, such as 2x + 3y = 5 and 4x + 6y = 10.

Real World Applications

Comparing two identical mobile data plans where one is advertised as 100 rupees for 1 GB and the other as 200 rupees for 2 GB, yielding the exact same cost graph.

Two temperature conversion formulas that are mathematically equivalent but written differently, plotting the exact same line on a graph.

Frequently Asked Questions

What is the condition for coincident lines in linear equations?

The condition is that the ratio of their corresponding coefficients must be equal, expressed algebraically as a1/a2 = b1/b2 = c1/c2.

Are coincident lines consistent or inconsistent?

Coincident lines form a consistent and dependent system of equations because they have infinitely many solutions.

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