Home » Ask & Discuss » Mathematics. » Algebra « Back to Discussion



Algebra

New kid on the Block

Joined: 9 May 2011
Post: 7
10 May 2011 19:52:24 IST
7 People liked this
9
696 View Post
statement-1: the function f(x)=x^2 e^-x^2 sin lxl is even statement-2: product of two odd functio
None

statement-1: the function f(x)=x^2 e^-x^2 sin lxl is evenstatement-2: product of two odd functions is an even function(1) statement 1 is true,statement 2 is true, statement 2 is not a correct explanation for statement 1(2) statement 1 is true,statement 2 is true, statement 2 is a correct explanation for statement 1


Share this article on:

Comments (9)

NugoRama's Avatar

Blazing goIITian

Joined: 11 Mar 2009
Posts: 5517
10 May 2011 21:56:00 IST
0 people liked this

 Its a tricky one so I'm not sure if I'll end up with the correct answer.

Obviously, both the statements are correct. And at first glance, we dont see any significant relation between the two statements.

Just for the sake of it, rewrite f(x) = x^2 e^-x^2 sin lxl as f(x) = x.(x e^-x^2 sin lxl) .. 

So, we have two odd functions now. And hence statement 2 is the correct explanation of statement 1.

My answer, (2).

GOPAKUMAR's Avatar

Scorching goIITian

Joined: 18 Mar 2010
Posts: 270
11 May 2011 12:55:16 IST
3 people liked this

 f(x)=x^2 e^-x^2 sin lxl

f(-x)=(-x)^2 e^-(-x)^2 sin l-xl => x^2 e^-x^2 sin lxl

therefore  f(x) = f(-x)

therefore even function

x^2 e^-x^2 sin lxl= x.(x e^-x^2 sin lxl)

since x is odd and x e^-x^2 sin lxl is also odd

but there product is a even function

 hence ans is  (2)


Scorching goIITian

Joined: 2 Mar 2011
Posts: 216
11 May 2011 13:54:26 IST
0 people liked this

ya agree to them
varun ganesh's Avatar

Scorching goIITian

Joined: 17 Jul 2010
Posts: 299
11 May 2011 14:51:13 IST
0 people liked this

so does it always mean product of two odd func. is always an even function?

NugoRama's Avatar

Blazing goIITian

Joined: 11 Mar 2009
Posts: 5517
11 May 2011 15:15:23 IST
0 people liked this

 Ofcourse, Varun.

Consider 2 odd functions f(x) and g(x).

Hence, f(-x) = - f(x) and g(-x) = - g(x)

f(-x)g(-x) = f(x)g(x) which makes their product an even function.

Thought of the day: Cloud nine gets all the publicity, but cloud eight actually is cheaper, less crowded, and has a better view.

varun ganesh's Avatar

Scorching goIITian

Joined: 17 Jul 2010
Posts: 299
11 May 2011 22:02:10 IST
0 people liked this

hw?

abu bakar's Avatar

Hot goIITian

Joined: 11 May 2011
Posts: 153
12 May 2011 00:26:17 IST
0 people liked this

two negatives make a positive but two wrongs never make a right..

varun ganesh's Avatar

Scorching goIITian

Joined: 17 Jul 2010
Posts: 299
12 May 2011 09:07:12 IST
0 people liked this

 @ abu bakar please elaborate.........!

GOPAKUMAR's Avatar

Scorching goIITian

Joined: 18 Mar 2010
Posts: 270
12 May 2011 11:08:28 IST
4 people liked this

 @varun ganesh 

 f(x)=x/lxl

g(x)=lxl/x

now f(x)*g(x)=1=h(x)

since it is a constant function

therefore h(-x)=1

therefore h(x) is a even function

therefore it is always true......




Quick Reply


Reply

Some HTML allowed.
Keep your comments above the belt or risk having them deleted.
Signup for a avatar to have your pictures show up by your comment
If Members see a thread that violates the Posting Rules, bring it to the attention of the Moderator Team
Free Sign Up!

Preparing for IIT-JEE ?

Arihant Revision Package for IIT JEE - Books, Practice Tests + Rank Predictor


@ INR 1,995/-

For Quick Info

Name

Mobile No.

Find Posts by Topics

Physics.

Topics

Mathematics.

Chemistry.

Biology

Parents

Board

Fun Zone

Sponsored Ads