In the expansion of (1+ax)n,nϵN,the coefficient of x and x2 are 8 and 24 respectively,then
A
a=2,n=4
Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses
B
a=4,n=2
No worries! We‘ve got your back. Try BYJU‘S free classes today!
C
a=2,n=6
No worries! We‘ve got your back. Try BYJU‘S free classes today!
D
a=−2,n=4
No worries! We‘ve got your back. Try BYJU‘S free classes today!
Open in App
Solution
The correct option is Aa=2,n=4 T3=nC2a2x2=24 T1=nC1ax=8 Taking the ratio we get nC2axn=3 (n−1)ax2=3 Since we are only taking the coefficients, we get a(n−1)=6 a=6(n−1) Substituting in the equation of T1 ,we get n(6n−1)=8 ⇒6n=8n−8 ⇒2n=8 ⇒n=4 Hence a=2.