Answer:
Option D
Explanation:
Given quadratic equations is x(x+1)+(x+1)(x+2)+.....+(x+¯n−1)(x+n)=10n
⇒ (x2+x2+....+x2)+[1+3+5+...+(2n−1)]x
+[1.2+2.3+...+(n−1)n]=10n
⇒ nx2+n2x+n(n2−1)3−10n=0
⇒ x2+nx+n2−13−10=0
⇒ 3x2+3nx+n2-31=0
Let α and β be the roots
Since, α and β are consecutive
∴ | α-β|=1
⇒ ( α -β)2=1
Again (α−β)2=(α+β)2−4αβ
⇒ 1=(−3n3)2−4(n2−313)
⇒ 1=n2−43(n2−31)
⇒ 3= 3n2−4n2+124
⇒ n2=121
⇒ n=± 11
∴ n=11 [ n>0]