Cramer’s rule :
The solution of the simultaneous equations
{ a 1 x + b 1 y = d 1 a 2 x + b 2 y = d 2 \begin{cases}
a_1x+b_1y=d_1
\\
a_2x+b_2y=d_2
\end{cases} { a 1 x + b 1 y = d 1 a 2 x + b 2 y = d 2
is given by the formulae
x = ∣ d 1 b 1 d 2 b 2 ∣ ∣ a 1 b 1 a 2 b 2 ∣ x=\frac{\begin{vmatrix}
d_1 & b_1 \\
d_2 & b_2
\end{vmatrix}
}{\begin{vmatrix}
a_1 & b_1 \\
a_2 & b_2
\end{vmatrix}} x = ∣ ∣ a 1 a 2 b 1 b 2 ∣ ∣ ∣ ∣ d 1 d 2 b 1 b 2 ∣ ∣ y = ∣ a 1 d 1 a 2 d 2 ∣ ∣ a 1 b 1 a 2 b 2 ∣ y=\frac{\begin{vmatrix}
a_1 & d_1 \\
a_2 & d_2
\end{vmatrix}
}{\begin{vmatrix}
a_1 & b_1 \\
a_2 & b_2
\end{vmatrix}} y = ∣ ∣ a 1 a 2 b 1 b 2 ∣ ∣ ∣ ∣ a 1 a 2 d 1 d 2 ∣ ∣
(i) { x − y = 0 x − y = 1 \begin{cases}
x-y=0
\\
x-y=1
\end{cases} { x − y = 0 x − y = 1
This system has no solution.
ii){ x − y = 0 x + y = 0 \begin{cases}
x-y=0
\\
x+y=0
\end{cases} { x − y = 0 x + y = 0
This system has a unique solution.
(iii) { x − y = 1 2 x − 2 y = 2 \begin{cases}
x-y=1
\\
2x-2y=2
\end{cases} { x − y = 1 2 x − 2 y = 2
This system has infinitely many solutions.
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