If ( 1+x2+x )10 ( 1+x2-x )9 dx= 1m ( ( 1+x2+x )n (n 1+x2-x ) )+C where C is the constant of integration and m, n N, then m+n is equal to .
Answer
379
Solution
Let t= 1+x2+x. Then 1+x2-x= 1t
1+x2= 12 (t+ 1t ), x= 12 (t- 1t )
dtdx= x 1+x2+1= t 1+x2 dx= 12 (1+ 1t2 )dt
I= t10 t9 12 (1+ 1t2 )dt= 12 (t19+t17 )dt
I= t2040+ t1836+C
Right side: n 1+x2-x= 12 [(n-1)t+ n+1t ]
1mtn (n 1+x2-x )= (n-1)tn+1+(n+1)tn-12m
Comparing: n+1=20 n=19
n-12m= 140 182m= 140 m=360
Check: n+12m= 20720= 136 (matches)
m+n=360+19=379
Answer: 379