Answer:
Option C
Explanation:
Here, to find the least value of αϵR . for which
4αx2+1x≥1, , for all x >0
i.e. to find the minimum value of α when
y=4αx2+1x;x>0 attains minimum value of α
∴ dydx=8αx−1x2 .....(i)
Now, d2ydx2=8α+2x3 ........(ii)
when dydx=0,
then 8x3α=1
d2ydx2=8α+16α=24α, Thus, y attains minimum when
x=(18α)13:α>0.
∴ y attains minimum when x=(18α)13
i.e, 4α(18α)23+(8α)13≥1
⇒α13+2α13≥1⇒3α13≥1
⇒ α≥127
Hence, the least value of α is 127