Question

Find the value of $(x-y)$, if $15x+17y=21$ and $17x+15y=11$.

Answer 1

The given equations are

$15x+17y=21\dots \dots \left(i\right)$

$17x+15y=11\dots \dots \left(ii\right)$

Now, subtracting equation $\left(i\right)$ from equation $\left(ii\right)$, we get

$\Rightarrow$ $17x+15y-(15x+17y)=11-21$

$\Rightarrow$ $17x+15y-15x-17y=-6$

$\Rightarrow 2x-2y=-6$

$\Rightarrow (x-y)=-3$