Using cross multiplication find the value of $x$ and $y$ for the equations:
$x + y = 7$ and $x - y = 9$

x = - 8, y = - 1

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x = 8, y = - 1

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x = 8, y = 1

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x = 8, y = 0

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Solution

The correct option is B $x = 8, y = - 1$
$x + y = 7$ ---(1)
$x - y = 9$ ---(2)
Using formula for cross multiplication method:
$\frac{x}{(b_{1} c_{2} - b_{2} c_{1})} = \frac{y}{(c_{1} a_{2} - a_{1} c_{2})} = \frac{- 1}{(a_{1} b_{2} - a_{2} b_{1})}$
So, from equation (1) and (2) we can write the value of $a, b$ and $c$ .
$\frac{x}{1 \times 9 - (- 1) \times 7} = \frac{y}{7 \times 1 - 1 \times 9} = \frac{- 1}{1 \times (- 1) - 1 \times 1}$
$\frac{x}{9 + 7} = \frac{y}{7 - 9} = \frac{- 1}{- 1 - 1}$
$\frac{x}{16} = \frac{y}{- 2} = \frac{- 1}{- 2}$ $, \frac{x}{16} = \frac{- 1}{- 2}$
$- 2 x = - 16$
$∴ x = 8$
$\frac{y}{- 2} = \frac{- 1}{- 2}$
$2 y = 2$
$∴ y = - 1$
Therefore, $x = 8, y = - 1$

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is [here

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Find the values of $x$ and $y$ if :

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Using cross multiplication find the value of x and y for the equations: x+y=7 and x−y=9

Using cross multiplication find the value of $x$ and $y$ for the equations:
$x + y = 7$ and $x - y = 9$