Question
The equations $$2x + 3y + 4 = 0; 3x + 4y + 6 = 0$$ and $$4x + 5y + 8 = 0$$ are
A.
consistent with unique solution
B.
inconsistent
C.
consistent with infinitely many solutions
D.
None of the above
Answer :
consistent with unique solution
Solution :
Consider first two equations :
$$2x + 3y = - 4$$ and $$3x + 4y = - 6$$
We have, \[\Delta = \left| {\begin{array}{*{20}{c}}
2&3\\
3&4
\end{array}} \right| = - 1 \ne 0\]
\[{\Delta _x} = \left| {\begin{array}{*{20}{c}}
{ - 4}&3\\
{ - 6}&4
\end{array}} \right| = 2\,\,{\rm{and }}\,\,{\Delta _y} = \left| {\begin{array}{*{20}{c}}
2&{ - 4}\\
3&{ - 6}
\end{array}} \right| = 0\]
∴ $$x = - 2$$ and $$y = 0$$
Now this solution satisfies the third, so the equations are consistent with unique solution.