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8. Sequences and Series
medium
If $f(x + y,x - y) = xy\,,$ then the arithmetic mean of $f(x,y)$ and $f(y,x)$ is
A
$x$
B
$y$
C
$0$
D
$1$
Solution
(c) Let $x + y = u,\,\,x – y = v$
==> $x = \frac{{u + v}}{2},y = \frac{{u – v}}{2}$,
$\therefore f(u,v) = \left( {\frac{{u + v}}{2}} \right).\left( {\frac{{u – v}}{2}} \right)$
Now,$\frac{{f(x,y) + f(y,x)}}{2} = \frac{{\left( {\frac{{x + y}}{2}.\frac{{x – y}}{2}} \right) + \left( {\frac{{y + x}}{2}.\frac{{y – x}}{2}} \right)}}{2} = 0$.
Standard 11
Mathematics