Consider the system of linear equations x+y+z=4 , x+2y+2 z=10 , x+3y+4 2z= 2+15 where , . Which one of the following statements is NOT correct ?
- The system has unique solution if 12 and 1, 15
- The system has infinite number of solutions if = 12 and =15
- The system is consistent if 12
- The system is inconsistent if = 12 and 1
Answer
(4) The system is inconsistent if = 12 and 1
Solution
= vmatrix1&1&1\\1&2&2 \\1&3&4 2 vmatrix=4 2-4 +1=(2 -1)2
12 0 unique solution (for every ) ⇒ (A), (C) are correct
= 12: x+y+z=4 , x+2y+z=10 , x+3y+z= 2+15
Subtracting successive equations: y=6 and y= 2-10 +15
2-16 +15=0 =1 or 15 (infinite solutions) ⇒ (B) is correct
(D): = 12, =15 ( 1) gives infinite solutions, not inconsistent ⇒ (D) is NOT correct
Answer: (4)