Solve using Cross multiplication Method:
\[\begin{array}{l}
x + y = 7\\
2x - 3y = 11
\end{array}\]
Answer
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Hint: If the two equation is in the form \[ax + by + c = 0\& dx + ey + f = 0\] then in cross multiplication method we write it as \[\dfrac{x}{{bf - ec}} = \dfrac{y}{{cd - af}} = \dfrac{1}{{ae - bd}}\] then use this to find the value of x and y respectively
Complete step by step answer:
The two equation we have are
\[\begin{array}{l}
x + y = 7\\
2x - 3y = 11
\end{array}\]
Which can also be written as
\[\begin{array}{l}
x + y - 7 = 0\\
2x - 3y - 11 = 0
\end{array}\]
Now if we compare this with \[ax + by + c = 0\& dx + ey + f = 0\]
We are getting \[a = 1,b = 1,c = - 7,d = 2,e = - 3,f = - 11\]
Now let us put all of these in
\[\dfrac{x}{{bf - ec}} = \dfrac{y}{{cd - af}} = \dfrac{1}{{ae - bd}}\]
So we will get
\[\begin{array}{l}
\therefore \dfrac{x}{{bf - ec}} = \dfrac{y}{{cd - af}} = \dfrac{1}{{ae - bd}}\\
\Rightarrow \dfrac{x}{{ - 11 \times 1 - ( - 3) \times ( - 7)}} = \dfrac{y}{{( - 7) \times 2 - 1 \times ( - 11)}} = \dfrac{1}{{1 \times ( - 3) - 2 \times 1}}\\
\Rightarrow \dfrac{x}{{ - 11 - 21}} = \dfrac{y}{{ - 14 - ( - 11)}} = \dfrac{1}{{ - 3 - 2}}\\
\Rightarrow \dfrac{x}{{ - 32}} = \dfrac{y}{{ - 3}} = \dfrac{1}{{ - 5}}\\
\Rightarrow \dfrac{x}{{32}} = \dfrac{y}{3} = \dfrac{1}{5}\\
\Rightarrow x = \dfrac{{32}}{5},y = \dfrac{3}{5}
\end{array}\]
So We are getting the value of x and y as \[\dfrac{{32}}{5}\] and \[\dfrac{3}{5}\] respectively.
Note: For cross checking put the values of x and y in both the equations given, for the first equation \[x + y - 7 = 0\] we will get \[\dfrac{{32}}{5} + \dfrac{3}{5} - 7\] which is 7-7 and that is basically zero, similarly if we put it in the second equation we will again get zero, which itself proves that our answers are correct.
Complete step by step answer:
The two equation we have are
\[\begin{array}{l}
x + y = 7\\
2x - 3y = 11
\end{array}\]
Which can also be written as
\[\begin{array}{l}
x + y - 7 = 0\\
2x - 3y - 11 = 0
\end{array}\]
Now if we compare this with \[ax + by + c = 0\& dx + ey + f = 0\]
We are getting \[a = 1,b = 1,c = - 7,d = 2,e = - 3,f = - 11\]
Now let us put all of these in
\[\dfrac{x}{{bf - ec}} = \dfrac{y}{{cd - af}} = \dfrac{1}{{ae - bd}}\]
So we will get
\[\begin{array}{l}
\therefore \dfrac{x}{{bf - ec}} = \dfrac{y}{{cd - af}} = \dfrac{1}{{ae - bd}}\\
\Rightarrow \dfrac{x}{{ - 11 \times 1 - ( - 3) \times ( - 7)}} = \dfrac{y}{{( - 7) \times 2 - 1 \times ( - 11)}} = \dfrac{1}{{1 \times ( - 3) - 2 \times 1}}\\
\Rightarrow \dfrac{x}{{ - 11 - 21}} = \dfrac{y}{{ - 14 - ( - 11)}} = \dfrac{1}{{ - 3 - 2}}\\
\Rightarrow \dfrac{x}{{ - 32}} = \dfrac{y}{{ - 3}} = \dfrac{1}{{ - 5}}\\
\Rightarrow \dfrac{x}{{32}} = \dfrac{y}{3} = \dfrac{1}{5}\\
\Rightarrow x = \dfrac{{32}}{5},y = \dfrac{3}{5}
\end{array}\]
So We are getting the value of x and y as \[\dfrac{{32}}{5}\] and \[\dfrac{3}{5}\] respectively.
Note: For cross checking put the values of x and y in both the equations given, for the first equation \[x + y - 7 = 0\] we will get \[\dfrac{{32}}{5} + \dfrac{3}{5} - 7\] which is 7-7 and that is basically zero, similarly if we put it in the second equation we will again get zero, which itself proves that our answers are correct.
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