Shortcut Trick
For linear equations to have no solution, the condition is: a1 / a2 = b1 / b2 ≠ c1 / c2.
Equating coefficients of x and y: 1 ÷ (1 − a) = −a ÷ 6 ⇒ a2 − a − 6 = 0 ⇒ a = 3 or −2.
Based on the given options, taking a = 3, the ratio becomes −3 ÷ 6 = −1/2.
Applying the inequality to constant terms: (2 − a) ÷ (a + b) ≠ −1/2.
Substituting a = 3 gives: −1 ÷ (3 + b) ≠ −1/2 ⇒ 3 + b ≠ 2 ⇒ b ≠ −1.
∴ The correct answer is a = 3, b ≠ -1.
Alternate Method
Given:
Equation 1: x − ay = 2 − a
Equation 2: (1 − a)x + 6y = a + b
Formula Used:
For a system of linear equations a1x + b1y = c1 and a2x + b2y = c2 to have no solution:
⇒ a1 / a2 = b1 / b2 ≠ c1 / c2
Calculations:
Comparing the given equations with standard form:
⇒ a1 = 1, b1 = −a, c1 = 2 − a
⇒ a2 = (1 − a), b2 = 6, c2 = a + b
Equating the ratios for no solution:
⇒ 1 / (1 − a) = −a / 6 ≠ (2 − a) / (a + b)
Solving the first part (equality):
⇒ 1 / (1 − a) = −a / 6
⇒ 6 = −a(1 − a)
⇒ 6 = −a + a2
⇒ a2 − a − 6 = 0
⇒ a2 − 3a + 2a − 6 = 0
⇒ a(a − 3) + 2(a − 3) = 0
⇒ (a − 3)(a + 2) = 0
⇒ a = 3 or a = −2
Since a = 3 is provided in the options, we proceed with a = 3.
Substituting a = 3 in the second part (inequality):
⇒ −a / 6 ≠ (2 − a) / (a + b)
⇒ −3 / 6 ≠ (2 − 3) / (3 + b)
⇒ −1 / 2 ≠ −1 / (3 + b)
⇒ 1 / 2 ≠ 1 / (3 + b)
Cross multiplying gives:
⇒ 3 + b ≠ 2
⇒ b ≠ 2 − 3
⇒ b ≠ −1
∴ The correct answer is a = 3, b ≠ -1.
Additional Information
Unique Solution
The system of equations has exactly one solution (lines intersect at exactly one point). Condition: a1 / a2 ≠ b1 / b2.
No Solution
The system of equations has no solution (lines are strictly parallel and never intersect). Condition: a1 / a2 = b1 / b2 ≠ c1 / c2.
Infinitely Many Solutions
The system of equations has infinitely many solutions (lines are coincident or overlap completely). Condition: a1 / a2 = b1 / b2 = c1 / c2.