x→2limn=1∑9(n(n+1)x2+2(2n+1)x+4x)
x→2limn=1∑9(n(n+1)x2+2nx+2(n+1)x+4x)
x→2limn=1∑9([(n+1)x+2][nx+2][(n+1)x+2]−[nx+2])
x→2limn=1∑9((nx+2)1−(n+1)x+21)
=x+21−2x+21
2x+21−3x+21
....x+21−10x+21+9x+21−10x+21
⇒x→2lim(x+21−10x+21)=449
⇒x→2lim(x+2)(10x+2)10x+2−x−2
x→2lim(x+2)(10x+2)9x=4×2218=449