# If 2x – 3y = 7 and (a + b) x – (a + b – 3) y = 4a + b represent coincident lines, then a and b satisfy the equationA. a + 5b = 0B. 5a + b = 0C. a – 5b = 0D. 5a – b = 0

Given:

Equation 1: 2x – 3y = 7

Equation 2:(a + b)x + (a + b – 3)y = 4a + b

Both the equations are in the form of :

a1x + b1y = c1 & a2x + b2y = c2 where

a1 & a2 are the coefficients of x

b1 & b2 are the coefficients of y

c1 & c2 are the constants

When two sets of linear equations which are coincident then they will have infinite number of solutions since both the equations represent the same line .So we have to use the conditions for the infinitely many number of solution.

For the system of linear equations to have infinitely many solutions we must have ………(i)

According to the problem:

a1 = 2

a2 = a + b

b1 = – 3

b2 = a + b – 3

c1 = 7

c2 = 4a + b

Putting the above values in equation (i) and solving the extreme left and middle portion of the equality

### The relationship between a and b for which the two equations represent coincident line is a = 5b or a – 5b = 0

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