If the system of equations
x - 2y + 3z = 9
2x + y + z = b
x - 7y + az = 24,
has infinitely many solutions, then a - b is equal to.........
Answer (integer)
5
Solution
D = 0<br><br>$$\left| {\matrix{
1 & { - 2} & 3 \cr
2 & 1 & 1 \cr
1 & { - 7} & a \cr
} } \right| = 0$$<br><br>$1(a + 7) + 2(2a - 1) + 3( - 14 - 1) = 0$<br><br>$a + 7 + 4a - 2 - 45 = 0$<br><br>$5a = 40$<br><br>$a = 8$<br><br>$${D_1} = \left| {\matrix{
9 & { - 2} & 3 \cr
b & 1 & 1 \cr
{24} & { - 7} & 8 \cr
} } \right| = 0$$<br><br>$\Rightarrow 9(8 + 7) + 2(8b - 24) + 3( - 7b - 24) = 0$<br><br>$\Rightarrow 135 + 16b - 48 - 21b - 72 = 0$<br><br>$\Rightarrow$ $15 = 5b$
<br><br>$\Rightarrow b = 3$<br><br>$a - b = 5$
About this question
Subject: Mathematics · Chapter: Matrices and Determinants · Topic: Types of Matrices and Operations
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