# Math Help - algebra problem

1. ## algebra problem

a,b>0, a+b=1, then prove that (a^2b)+(b^2a)<=1

2. ## Re: algebra problem

Originally Posted by Swarnav
a,b>0, a+b=1, then prove that (a^2b)+(b^2a)<=1
If a + b = 1 then we know that b = 1 - a. So we have
$a^2b + b^2 a = a^2 (1 - a) - (1 - a)^2$

Simplifying we eventually get
$a^2b + b^2 a = a^2 - a$

Now, you can probably find a more elegant way to prove that $-a^2 + a \leq 1$, but the simplest way to approach this is to simply graph it.

-Dan

3. ## Re: algebra problem

it is not (a^2)*b or(b^2)a,it is a^(2b)+b^(2a)

4. ## Re: algebra problem

please someone help me to solve it.

5. ## Re: algebra problem

a,b>0, a+b=1, then prove that (a^2b)+(b^2a)<=1

a+ b =1 are given
then
a= 1-b
multiply a both side

a^2 = a -a*b
multiply b both side
a^2 *b = ab -a* b^2
then
a^2 *b + b^2 *a = ab
a,b>0 & a+b =1 are given
then ab>=1

then we can say that
(a^2b)+(b^2a)<=1

hence proved

6. ## Re: algebra problem

I think this is the right ans...............
if u know something diff..............
plz share with whole team.........
Regards
prem

7. ## Re: algebra problem

a^2b+b^2a=ab(a+b)=ab
according to the basic inequelity:a>0,b>0,so√ab≤（a+b）/2=1/2
we see the original polynomial=ab=(√ab)^2≤1/4
the restriction of problem is so loose that we can suspect there are some other ways to solve it

8. ## Re: algebra problem

Hi CosmoBlazer !
This solution is too good.I did not think such type of logic .....
this is the more easy and time less solution...............

thanks

9. ## Re: algebra problem

if u have something other easiest evaluation ..

thanks

10. ## Re: algebra problem

Originally Posted by pssingh1001
a,b>0, a+b=1, then prove that (a^2b)+(b^2a)<=1

a+ b =1 are given
then
a= 1-b
multiply a both side

a^2 = a -a*b
multiply b both side
a^2 *b = ab -a* b^2
then
a^2 *b + b^2 *a = ab
a,b>0 & a+b =1 are given
then ab>=1

then we can say that
(a^2b)+(b^2a)<=1

hence proved
When a + b = 1 and a,b >0 then ab <=0
Then we can conclude that (a^2b)+(b^2a)<=1