ax+2y=5, 3x−6y=20. In the system of equations above, a is a constant. If the system has one solution, which of the following CANNOT be the value of a?

by

A. 6
B. -1
C. -5
D. 4

🧠 Explanation (Math):

Given: ax + 2y = 5 and 3x − 6y = 20; one solution ⇒ determinant ≠ 0
Step 1: Determinant D = a(−6) − 3(2) = −6a − 6
Step 2: Require D ≠ 0 ⇒ −6a − 6 ≠ 0 ⇒ a ≠ −1
Step 3: Thus the value that cannot occur (violates one-solution condition) is −1
Final Answer: −1