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Solve the following pair of linear equations by the substitution and cross-multiplication methods:
$8x + 5y = 9$
$3x + 2y = 4$
Given:
$8x + 5y = 9$
$3x + 2y = 4$
To do:
We have to solve the given pair of linear equations by the substitution and cross-multiplication methods.
Solution:
By substitution method:
$8x+5y=9$
This implies,
$x=\frac{9-5y}{8}$.....(i)
$3x+2y=4$
$3(\frac{9-5y}{8})+2y=4$ [From (i)]
$\frac{27-15y}{8}=4-2y$
$27-15y=8(4-2y)$
$27-15y=32-16y$
$16y-15y=32-27$
$y=5$
Therefore,
$x=\frac{9-5(5)}{8}$
$x=\frac{9-25}{8}$
$x=\frac{-16}{8}$
$x=-2$
By cross multiplication method,we get,
$\frac{x}{5(4)-(2)(9)}=\frac{y}{9(3)-(4)(8)}=\frac{-1}{8(2)-3(5)}$
$\frac{x}{20-18}=\frac{y}{27-32}=\frac{-1}{16-15}$
$\frac{x}{2}=\frac{-1}{1}$ and $\frac{y}{-5}=\frac{-1}{1}$
$x=-1(2)$ and $y=-1(-5)$
$x=-2$ and $y=5$
The values of $x$ and $y$ are $-2$ and $5$ respectively.
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