Question

If 3x+4y=18 and 4x+3y=17 find the value of x-y

Answer 1

$\huge\textbf\green{Answer :}$

3x + 4y = 18 ...... (1)

4x + 3y = 17 ...... (2)

Multiply (1) by 4 and (2) by 3. Then we get;

12x + 16y = 72 ..... (3)

12x + 9y = 51 ..... (4)

Solve (3) and (4) by elimination...

12x + 16y = 72
12x + 09y = 51 [Change the signs]
____________
00x + 07 y = 21
____________

7y = 21

$y$ = $\dfrac{21}{7}$

$y$ = $3$

Put value of y in (1)

3x + 4(3) = 18

3x + 12 = 18

3x = 6

$x$ = $\dfrac{6}{3}$

$x$ = $2$

We have to find the value of x - y

So,

x - y = 2 - 3

$\textbf{x - y = - 1}$

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Answer 2

3x + 4y =18
4(3x+4y)= 18*4
12x +16y =72. (1)......

4x + 3y =17
3(4x+3y) = 17*3
12x + 9y= 51. (2)......

from (1) and (2)
12x-12x +16y -9y = 72-51
7y = 21
y = 3
4x + 3(3) = 17
4x = 17-9
4x = 8
X = 2
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