correct answer is: a) 0

Explanation

Here KaTeX parse error: KaTeX doesn't work in quirks mode.
KaTeX parse error: KaTeX doesn't work in quirks mode. _{[L.C.M ‘ab’]}
KaTeX parse error: KaTeX doesn't work in quirks mode. _{[cross multiply]}

We know,
KaTeX parse error: KaTeX doesn't work in quirks mode.
KaTeX parse error: KaTeX doesn't work in quirks mode. _{[put the value of a²+b²]}
KaTeX parse error: KaTeX doesn't work in quirks mode.
KaTeX parse error: KaTeX doesn't work in quirks mode.
Ans: KaTeX parse error: KaTeX doesn't work in quirks mode.