The correct option is B 0
f(x)=[x]sin2(πx)
f(x)=⎧⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪⎨⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪⎩−7sin2(πx),x∈(−7,−6)0,x=−6−6sin2(πx),x∈(−6,−5)0,x=−5………………0,x=99sin2(πx),x∈(9,10)
Clearly f(x) is continuous for x∈(−7,10)
f′(x)=⎧⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪⎨⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪⎩−7sin(2πx),x∈(−7,−6)0,x=−6−6sin(2πx),x∈(−6,−5)0,x=−5………………0,x=99sin(2πx),x∈(9,10)
Clearly f(x) is differentiable for x∈(−7,10)
Hence, there is no such point where f(x) is not differentiable for x∈(−7,10)