若a=m分之n+n分之m,b=m分之n-n分之m,求a平方-b平方的值

若a=m分之n+n分之m,b=m分之n-n分之m,求a平方-b平方的值

a = n/m +m/n
b = n/m -m/n
a²;-b²;
=(a+b)(a-b)
=(n/m +m/n+n/m -m/n)(n/m +m/n -n/m +m/n)
= 2n/m×2m/n
= 4