If a + b + c = 0 and a b c = 0 , find the value of a 2 b 2 + b 2 c 2 + c 2 a 2 a 4 + b 4 + c 4
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
@Anik Mandal I like your solution nice !!!
Log in to reply
Then please upvote it.....I haven't had a single upvote since the last two weeks!So please... @Mardokay Mosazghi
nyce approach bro
Knowing the actual source,
With S = a + b + c, P = a b c and I = 1/ a + 1/ b + 1/ c,
a^4 + b^4 + c^4 = S^4 - 4 P I S^2 + 4 P S + 2 P^2 I^2
S = a + b + c = 0:
a^4 + b^4 + c^4 = 2 P^2 I^2 = 2 (b c + c a + a b)^2
(a^4 + b^4 + c^4)/ (a^2 b^2 + b^2 c^2 + c^2 a^2)
= 2 + 4 a b c (a + b + c)/ (b^2 c^2 + c^2 a^2 + a^2 b^2)
= 2
a + b + c = 0 Squaring both sides we get :
a 2 + b 2 + c 2 + 2 a b + 2 b c + 2 a c = 0
Rearranging we get :
a 2 + b 2 + c 2 = − 2 ( a b + b c + a c ) again squaring both sides we get :
a 4 + b 4 + c 4 + 2 ( a 2 b 2 + a 2 c 2 + b 2 c 2 ) = 4 ( a 2 b 2 + a 2 c 2 + b 2 c 2 + 2 a b c ( a + b + c ) )
Using a + b + c = 0 and rearranging some terms we get :
a 4 + b 4 + c 4 = 2 ( a 2 b 2 + a 2 c 2 + b 2 c 2 )
Finally a 2 b 2 + a 2 c 2 + b 2 c 2 a 4 + b 4 + c 4 = 2
But if you take values all as 0, then the answer is 0. The answer to this question is 0 not 2.
Log in to reply
No no no no no no the denominator will become 0. No no no no no no no
I agree with your argument but in these types of questions you have to solve them using variables instead of no.s just like Ronak Agarwal has done
However ther is even a smarter way to solve it
Log in to reply
But you should have mentioned that a,b,c are not equal to 1.
Log in to reply
@Anuj Shikarkhane – If you take a=b=c=0, Then your answer will come as 0/0. Remember 0/0 is undefined so the answer can come as 1,2,3,....... This happens as 0* any no is 0. So we can put any no. in the answer if there is 0/0.
People I have been getting many notifications on clarification of the case if we take 0. I would like to tell you if we take a,b and c as 0, the situation comes out to be 0/0. Remember 0/0 is not defined as any no. divided by 0 is undefined so 0/0 can be any answer so in these questions we don't take it as 0/0 as answer. By the way 0/0 can also be the answer too. I hope I have cleared your doubt but do comment if it still persists and the way Anik Mandal solved is just the way you do it. Do share your different method of solving it:)
its simple for this problem does'nt need to think big take 3 values satisfying a+b+c=0 as a=2 b=-1 c=-1 thats it we get solution easily
a + b + c = 0
(a + b + c)^2 = 0
a^2 + b^2 + c^2 + 2(ab + bc + ac) = 0
a^2 + b^2 + c^2 = -2 (ab + bc + ac)
[a^2 + b^2 + c^2]^2 = [-2 (ab + bc + ac)]^2
a^4 + b^4 + c^4 + 2[a^2.b^2 + b^2.c^2 + a^2.c^2] = 4[a^2.b^2 + b^2.c^2 + a^2.c^2 + 2abc (a + b + c ) ]
But a + b + c = 0 a^4 + b^4 + c^4 + 2[a^2.b^2 + b^2.c^2 + a^2.c^2] = 4[a^2.b^2 + b^2.c^2 + a^2.c^2]
a^4 + b^4 + c^4 = 2[a^2.b^2 + b^2.c^2 + a^2.c^2]
Hence, a^4 + b^4 + c^4 / [a^2.b^2 + b^2.c^2 + a^2.c^2] = 2
Put any three numbers a,b,c such that a+b+c = 0, and you'll get same answer in each case!! That's because its actually an identity in a,b,c for all real a+b+c = 0. This method is meant only to get quick answers and is not actual solution to the problem.
a+b+c = 0 --> a+b = -c -->(a+b)^4 = (-c)^4 -->a^4 + (4a^3)b + (6a^2)(b^2) + 4ab^3 + b^4 = c^4
a^4 + b^4 + c^4 --> a^4 + b^4 + a^4 + (4a^3)b + (6a^2)(b^2) + 4ab^3 + b^4 = 2a^4 + (4a^3)b + (6a^2)(b^2) + 4ab^3 + 2b^4
(a+b)^2 = (-c)^2 -->(a^2 + 2ab + b^2) = c^2 -->(a^2)(b^2) + (b^2)(c^2) + (c^2)(a^2) --> (a^2)(b^2) + (a^2 + 2ab + b^2)b^2 + a^2(a^2 + 2ab + b^2) = a^4 + (2a^3)b + (3a^2)(b^2) + 2ab^3 + b^4
So, there fore... (2a^4 + (4a^3)b + (6a^2)(b^2) + 4ab^3 + 2b^4)/(a^4 + (2a^3)b + (3a^2)(b^2) + 2ab^3 + b^4)
= 2 (Q.E.D)
the solution given by ronak agarwal is often used... if u don't follow his method, you can take a=1 b=-1 and c=0 or any other solution set where a+b+c=0 then also u will get "2"
I used exact same example. ..
Problem Loading...
Note Loading...
Set Loading...
a + b + c = 0
a + b = − c
a 2 + b 2 + 2 a b = c 2
a 2 + b 2 − c 2 = − 2 a b
( a 2 + b 2 − c 2 ) 2 = 4 a 2 b 2
a 4 + b 4 + c 4 + 2 a 2 b 2 − 2 b 2 c 2 − 2 c 2 a 2 = 4 a 2 b 2
a 4 + b 4 + c 4 = 2 a 2 b 2 + 2 b 2 c 2 + 2 c 2 a 2
a 4 + b 4 + c 4 = 2 ( a 2 b 2 + b 2 c 2 + c 2 a 2 )
Hence,the result of the given expression is 2.