Directions: In the following questions, A statement of Assertion (A) ...
Let us first consider the assertion. It says that the linear equations x − 2y − 3 = 0 and 3x + 4y − 20 = 0 have exactly one solution.
Let x − 2y − 3 = 0--- (1) And, 3x + 4y − 20 = 0---(2)
In order to solve these equations, let us multiply the first equation by 3.
3(x − 2y − 3) = 3 × 0
⟹ 3x − 6y − 9 = 0 ----(3)
Subtracting equation 3 from equation 2, we get,
3x + 4y − 20 − (3x − 6y − 9) = 0
Removing the brackets, we get,
3x + 4y − 20 − 3x + 6y + 9 = 0
⟹ 10y − 11 = 0
⟹ y = 11 / 10
Now, in order to find the value of x, substituting the value of y in equation 1, we get,
Thus, the pair of linear equations given possess exactly one solution (unique solution).
Hence, the assertion is correct.
Now, let us consider the reason. It says that the linear equations 2x + 3y − 9 = 0 and 4x + 6y − 8 = 0 have a unique solution.
Let 2x + 3y − 9 = 0---(1)
And, 4x + 6y − 18 = 0---(2)
In order to solve these equations, let us multiply the first equation by 2.
2(2x + 3y − 9) = 2 × 0
⟹4x + 6y − 18=0---(3)
As, equation 2 and 3 are same thus, thus the two linear equations given to us are coincident possessing infinitely many solutions.
Thus, the reason is not correct.
Thus, Assertion is correct but the Reason is incorrect.