IIT JEE 2008 P1 Q18-20

q.18 dy/dx=1/3(1-y²)

d²y/dx²=2y/9(1-y²)³

at x=-10√2 y=2√2

then d²y/dx² at x=-10√2 = f"(-10√2)=-4√2/9x7³=-4√2/7³x3²

hence option b

q.20

y³-3y+x=0 x(-2,2)

for a given function if (a,b) lies on it then (-a,-b) will also lie because g(x) is odd

g(-1)=-g(1) and g(0)=0

\int_{-1}^{1}{g'(x)dx}=2\int_{0}^{1}{g'(x)dx}=2g(1)

hecne option d