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The number of integers $a$ in the interval $[1,2014]$ for which the system of equations $x+y=a$, $\frac{x^2}{x-1}+\frac{y^2}{y-1}=4$ has finitely many solutions is
$0$
$1007$
$2013$
$2014$
Solution
(d)
Given,
$x+y=a \Rightarrow a \in[1,2014]$
and $\frac{x^2}{x-1}+\frac{y^2}{y-1}=4$
$\therefore \quad \frac{x^2}{x-1}+\frac{y^2}{y-1}=4$
$\Rightarrow x^2 y-x^2+x y^2-y^2=4(x-1)(y-1)$
$\Rightarrow x^2 y+x y^2=4(x y-(x+y)+1)+x^2+y^2$
$\Rightarrow \quad x y(x+y)=4(x y-a+1) +(x+y)^2-2 x y$
$\Rightarrow \quad x y(a)=4 x y-4 a+4+a^2-2 x y$
$\Rightarrow \quad x y a-2 x y=a^2-4 a+4$
$\Rightarrow x y \quad(a-2)=(a-2)^2$
$\Rightarrow \quad(a-2)^2-x y(a-2)=0$
$\Rightarrow \quad(a-2)(a-2-x y)=0$
$a=2$ or $x y=a-2$
$x(a-x)=a-2 \quad[\because y=a-x]$
$x^2-a x+a-2=0$
$\Rightarrow(a \times b)(c+1)+b(c+1)+a(c+1)+(c+1)=30$
$\Rightarrow(c+1)(a \times b+b+a+1)=30$
$\Rightarrow(c+1)(b(a+1)+1(a+1))=30$
$\Rightarrow \quad(a+1))(b+1)(c+1)=30$
$1 \leq a \leq 9,0 \leq b, c \leq 9$
$\because$ Total number of solution $=18$