We know that the denominator can be distributed in a fraction like c a + b = c a + c b
But you can't do this in b + c a = b a + c a It will be a mistake if you do it.
But for how many triples ( a , b , c ) of positive integers is the above (second equation) property true?
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.
I did it in this way (considering a,b,c as non-zero reals).
Lets assume that for a triple ( a , b , c ) , the equation b + c a = b a + c a holds true.
After a little calculation and cancelling out a from both sides since it's non-zero, we get,
b 2 + c 2 + b c = 0
Now, since b 2 and c 2 are always positive, we should have b c = 0 and thus the solution would be b = 0 or c = 0 or b = 0 ∧ c = 0 .
But a , b , c are non-zero reals. So, our original assumption was wrong. Thus, there exists no triple ( a , b , c ) , a , b , c ∈ R − { 0 } that satisfies the given equation.
Log in to reply
Same solution. For the equation to be true, either b or c must be negative.
Log in to reply
Not quite. There exists no triple ( a , b , c ) of non-zero reals a , b , c that satisfy the given equation. So, even for negative values of b , c , there doesn't exist any non-zero real a satisfying the equation.
Log in to reply
@Prasun Biswas – Since both b 2 and c 2 are positive, how can b 2 + c 2 + b c be equal to 0 ? Only by either b = c = 0 or b = − ( 2 1 ± 3 i ) × c .
Log in to reply
@Roman Frago – You meant that kind of negative? I thought you meant negative real. You should've said that you're considering non-real numbers then. My method explicitly assumed a , b , c as non-zero reals (hence I didn't think about non-real complex values). Sorry for the misunderstanding.
If you're given that a is non-zero, then there can be no ordered triple [they dont even have to be integers] even if you allow b and c to be negative.
Log in to reply
But i wanted to give the condition only on a (when it gets positive it's non-zero) but to make it look better, i gave to all ...
Log in to reply
First, note that we can divide both sides by a . Now, if there existed a solution to b , c , then there would be an infinite number of solutions, since we can take a to be any positive integer. Thus there are no solutions.
Correct. No real number would satisfy the equation if a = 0 .
Wow... that's a cool set you've shared.
Working the expression and you'll get that the only possible solution could be when a ( c 2 + b c + b 2 ) = 0 But a can't be 0, because the triples may only be positive integers. Note that c 2 + b c + b 2 = 0 if both b and c ar equal to 0, that's impossible because c can't be replaced by 0 on the first expression
Thus, there are no triples of positive integers such that the statement is true
bc=(b+c)^2 b^2+bc+c^2=0 This cannot be '0' for any positive values of b and c
so the no.of triplets = 0
oh.......... I see, thanks!!!
Since a , b & c are all positive integers : b + c a = b a + c a
By multiplying both sides by a 1 , we get : b + c 1 = b 1 + c 1 ∴ b b + c + c b + c = 1 = b b + b c + c b + c c = b c + c b + 2 ∴ b c + c b = − 1 ∴ b c c 2 + b c b 2 = b c b 2 + c 2 = − 1 ∴ b 2 + c 2 = − b c
But as we see , as both b and c are positive integers , Hence b 2 + c 2 is a positive value and also − b c is a negative value . Which leads us to a contradiction and an impossible argument .
And thus , there is no triple ( a , b , c ) (given the above conditions) satisfying the equation . And the answer is 0 .
b + c a = b a + c a b + c 1 = b 1 + c 1 b + c 1 = b c b + c b c = b 2 + 2 b c + c 2 b 2 + b c + c 2 = 0
The equation above cannot be true for any positive integer as square of any positive integer is always positive. Also since both b and c are positive, b c will always be positive.
Hence no triplet satisfies the equation.
You should still add a line about why it cannot be true for any positive integer.
Same way!!
Note that if there was a triple (a,b,c) that worked, then we could replace a with any other positive integer in order to make another working triple. But this would mean the answer is infinitely many and that can't be inputted, so the answer must be 0 :D.
But I actually did it the way it was meant to be in order to make sure i was right.
Problem Loading...
Note Loading...
Set Loading...
Because the triples are of positive integers, we can cancel out a from the numerator, because a = 0 as a is asked to be POSITIVE INTEGER.
Thus we get b + c 1 = b 1 + c 1 .
But because b and c are also positive integers, we can say that b + c > b ⟹ b + c 1 < b 1 a n d b + c > c ⟹ b + c 1 < c 1
And this results in b + c 1 < b 1 + c 1 . . . . . . . . . . . ∀ b , c ∈ N
Thus the required statement is not true for any triples ( a , b , c ) , hence the answer is 0