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Q.

Let f(x) be a non-constant, twice differentiable function defined on R such that y=f(x) is symmetric about line x = 1 and  f(1)=f'(14)=f'(12)=0, then which of following statement(s) is (are) TRUE?

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a

For some  c(1,32),f'(c)=cf"(c)

b

There exist at least one c(32,74) such that  f'(c)+cf"(c)=0

c

22(x5+x3)f(1+x)dx<0211+2f(x)dx

d

f"(x)=0  has atleast four roots in the interval (0,2) 

answer is A, B, C, D.

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Detailed Solution

f(1x)=f(1+x)  f'(1x)+f'(1+x)=0        put, x=0f'(1)=0     Given,  f'(14)=0f'(74)=0        f'(12)=0f'(32)=0

applying Rolle’s theorem in (14,12),(12,1),(1,32),(32,74) 
f"(x)=0  has at least 4 roots in (0, 2)
(A)

I=22(x5+x3)f(1+x)dx          I=22((x)5+(x)3)f(1x)dxI+I=22f(1+x)×0dx=0

I=0<0211+2f(x)dx(B)

SupposeF(x)=f'(x)x

F(1)=F(32)=0

Applying Rolles theorem
F'(c)=0 for at least one c in  (1,32)
c.f"(c)f'(c)=0 c.f"(c)=f'(c)

for at least one c in  (1,32)
Suppose G(x)=x.f(x)

G(32)=G(74)=0       G'(x)=1.f'(x)+xf"(x)

Applying Rolle’s theorem in  (32,74)
f'(c)+cf"(c)=0 for at least one c in  (32,74)

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