Rolle's Theorem/ Lagrange's Mean value theorem Sikho....

Q 1) Prove that f(x)=\frac{x^7}{7}-\frac{x^6}{6}+\frac{x^5}{5}-\frac{x^4}{4}+\frac{x^3}{3}-\frac{x^2}{2}+x-1 has exactly one real root

Q 2) In 1 hour a snail travels 60 meters. Prove that there was an Interval of 10 minutes where it traveled exactly 10 meters. (Not exactly Rolle's Theorem)

Q 3) Prove that f(x)=x3 - 3x + c never has both its roots in [0,1]

Q 4) if f(x)= ax3+bx2+cx+d, a≠0, Prove that f(x) cannot have more than one real roots, if b2<3ac

Q 5) Prove that there exists c in (a,b) such that f(c)f'(c)=c, given f is differentiable on (a,b) and f2(a)-f2(b)=a2-b2

Q 6) Let f is a continuous function on [a,b]

Prove that exists c in (a,b) such that \int_a^cf(x)\ \mathrm{dx}=(b-c)f(c)

Q 7) Prove LMVT using Rolle's Theorem

Q 8) Give an example to show that continuity in [a,b] and not just (a,b) is a necessary condition for both Rolle's and LMVT

Q 9) f and g are real functions continuous on [a,b] and differentiable on(a,b).
Show that there exists c in (a,b) such that f'(c)(b-c)+g'(c)(c-a)=(f(c)-f(a))+(g(b)-g(c))

Q 10) Let f , g continuous functions on [a , b] with f'(x)≠0 in (a , b).
Prove that there exists c in (a,b) such that : \frac{f'(c)}{f(a)-f(c)}+\frac{g'(c)}{g(b)-g(c)}= 1

39 Answers

62
Lokesh Verma ·

Q 11) Let f(x) continous in [a,b] satisfying the condition: \int^b_a f(x)dx=0
Show that there exists c in (a,b) such that:f(c)=2005 \int^c_a f(x)dx

Q 12) can we say that the result in 11 is true for any value or number other than 2005?

341
Hari Shankar ·

msp your explanation for Q2 is not correct, because we need to show that there is an interval where the average speed was 1, not that the instantaneous velocity at a point is 1.

You will need a concept called the Universal Chord Theorem for this one

62
Lokesh Verma ·

Prophet sir, I think it can be done without that too...

just by constructing a function alone :)

Basically the function will use the idea of the proof :)

341
Hari Shankar ·

that proof using the function u have in mind is the proof of the Universal Chord Theorem.

62
Lokesh Verma ·

yes i had never seen the universal chord theorem..

I just read it now after reading your post... and realized that the proof is the same as the function i had thought of :)

That is why i was wondering why i had not seen this kind of a problem when i was preparing!

3
msp ·

okie sir.Even i know that it is rong,i have given my contribution,so that i can get corrections from users.Thanq for correcting.

39
Dr.House ·

what happened to post # 8 nishant bhaiyan ? u think its wrong???

shall i prove that??

62
Lokesh Verma ·

no you dont need to prove it.. i just overlooked that one :)

1
RAY ·

let us assume the given eqn has all roots real...so every equation we get after differentiating it will ahev real roots ....

1.differentiating given equation 5 times we get

15x2-5x+1=0
hence the roots are imaginary...so the given equations will have max possible even number of roots imaginary....hence only 1 real root

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