JEE MAIN - Mathematics (2018 - 16th April Morning Slot - No. 9)
The number of values of k for which the system of linear equations,
(k + 2)x + 10y = k
kx + (k +3)y = k -1
has no solution, is :
(k + 2)x + 10y = k
kx + (k +3)y = k -1
has no solution, is :
1
2
3
infinitely many
Explanation
System of linear equation have no solution,
$$\therefore\,\,\,$$ determinant of coefficient = 0
$$\left| {\matrix{ {k + 2} & {10} \cr k & {k + 3} \cr } } \right| = 0$$
$$ \Rightarrow $$ $$\,\,\,\,$$ (k + 2) (k + 3) $$-$$ 10 K = 0
$$ \Rightarrow $$ $$\,\,\,\,$$ k2 $$-$$ 5k + 6 = 0
$$\therefore\,\,\,\,$$ k = 2, 3
When, k = 2 then equations become,
4x + 10y = 2
and 2x + 5y = 1
It has in finite number of solutions.
When k = 3, equations becomes
5x + 10y = 3
3x + 6y = 2
Those equation has no solutions.
$$\therefore\,\,\,\,$$ When k = 3, then system of equations have no solutions.
$$\therefore\,\,\,$$ determinant of coefficient = 0
$$\left| {\matrix{ {k + 2} & {10} \cr k & {k + 3} \cr } } \right| = 0$$
$$ \Rightarrow $$ $$\,\,\,\,$$ (k + 2) (k + 3) $$-$$ 10 K = 0
$$ \Rightarrow $$ $$\,\,\,\,$$ k2 $$-$$ 5k + 6 = 0
$$\therefore\,\,\,\,$$ k = 2, 3
When, k = 2 then equations become,
4x + 10y = 2
and 2x + 5y = 1
It has in finite number of solutions.
When k = 3, equations becomes
5x + 10y = 3
3x + 6y = 2
Those equation has no solutions.
$$\therefore\,\,\,\,$$ When k = 3, then system of equations have no solutions.
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