x=ab=10a+b y=ba=10b+a(1≤a,b≤9) x2−y2=m2 100a2+b2+20ab−(100b2+a2+20ab)=m2 99(a2−b2)=m2 9×11×(a−b)(a+b)=m2 m is integer so a = 6 {Note: a – b ≠9 (think why ?)} b = 5 m2=9×11×1×11⇒m=3×11 x+y+m=10a+b+10b+a+33 =11(a+b)+33=11(11)+33=121+33=154