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Questions  

If f(x)=kx39x2+9x+3is monotonically increasing in R, then

a
k<3
b
k≤3
c
k≥2
d
none of these

detailed solution

Correct option is C

f′(x)=3kx2−18x+9=3kx2−6x+3≥0∀x∈R or  D=b2−4ac≤0,k>0, i.e., 36−12k≤0 or    k≥3

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