RRB Group-D Model Paper 17 with answers for online practice

GIVEN:
x – y = 12 and ${\mathit{x}}^2+{\mathit{y}}^2$ = 156
CONCEPT:
Here we need to carefully look at the question and check whether ${\left(\mathit{x}+\mathit{y}\right)}^2\mathit{o}\mathit{r}{\left(\mathit{x}\mathit{–}\mathit{y}\right)}^2$ will be applied
FORMULAE USED:
${\left(\mathit{x}\mathit{–}\mathit{y}\right)}^2$ = ${\mathit{x}}^2+{\mathit{y}}^2$ – 2xy
CALCULATION:
Considering the given statement
x – y = 12 and ${\mathit{x}}^2+{\mathit{y}}^2$ = 156
${\left(\mathit{x}\mathit{–}\mathit{y}\right)}^2=\mathit{x}2+\mathit{y}2$ – 2xy
Putting the values we get,
${\left(12\right)}^2={\mathit{x}}^2+{\mathit{y}}^2\mathit{–}2\mathit{x}\mathit{y}$
⇒ 144 = 156 – 2xy
⇒ 2xy = 12
⇒ xy = 6
∴ Required value is 6