We have,
(1−y)m(1+y)n
=(C0m−C1my+C2my2+...+Cmm(−1)mym)(C0n+C1ny+C2ny2+...+Cnnyn)
Coefficient of y(a1)=1⋅C1n+C1m(−1)
=n−m=10…(1)
Coefficient of y2(a2)
=1C2n−C1mC1n+1mC2=10
⇒2n(n−1)−m⋅n+2m(m−1)=10
⇒m2+n2−2mn−(n+m)=20
⇒(n−m)2−(n+m)=20
⇒n+m=80…(2)
By equation (1) and (2)
m=35,n=45
Hence, m+n=80