1 .
THE ANS IS
x = \frac{a^2 + b^2 }{a+ b}
posting the complete solution
on slight rearrangement
\frac{x - a}{b} - \frac{b}{x- a} = \frac{a}{x- b }-\frac{x-b}{a}
\frac{\left(x- a \right)^ 2 - (b^2) }{b \left(x- a \right)} = \frac{a^ 2 - \left(x-b \right)^ 2}{( x- b). a}
again rearranging we get
\frac{\left(x- a \right)^ 2 - (b^2) }{(a^ 2) - \left(x- b \right)^2 } = \frac{b (x-a)}{a( x- b). }
now use a^ 2 - b^2 pharmoola
\frac{\left(x- a+ b \right)\left(x- a- b \right)}{\left(a+ x- b \right)\left(a-x + b \right)} = \frac{\left(x-a + b \right)(x - a- b )}{\left(a + x - b \right)\left(-( -a + x- b) \right)}
\frac{ x- a + b }{-a - x+ b } = \frac{b\left(x-a \right)}{a\left(x-b \right)}
now on rearranging we get
( x- a + b )a ( x- b) = b ( x- a ) .( b- a - x )
simplifying both sides
( ax - a^2 + ab ) ( x- b) = ax^2 - axb - a^ 2x + a^2 b + abx - ab^2
---1
( b^2 - ba - bx ) ( x- a ) = b^ 2x - b^2a - bax + ba^2 - bx^2 + bax---2
equate 1 and 2
ax^ 2 - a^ 2 x + a^2 b - ab^2 = b^2 x - bx^2 + a^2b - ab^2
ax^ 2 - a^ 2 x = b^2 x - bx^2
ax - a^2 = b^2 - bx
ax + bx = a^2 + b^2
x ( a + b ) = a^2 + b^2
x =\frac{a^2 + b^2 }{ a+ b}