system of equations solving for positive a , b , c ( 1 &#x2212;<!-- − -

Elisha Kelly

Elisha Kelly

Answered question

2022-05-27

system of equations solving for positive a , b , c
( 1 a ) ( 1 b ) ( 1 c ) = a b c
a + b + c = 1
I found that 0 < a , b , c < 1 and I try to solve it by try ( 1 a ) = a, ( 1 b ) = b and ( 1 c ) = c and got that a = 0.5 , b = 0.5 , c = 0.5 but it contradicts the second equations.

Answer & Explanation

aqueritztv

aqueritztv

Beginner2022-05-28Added 10 answers

by expanding the left hand side you will have
1 ( a + b + c ) + a b + b c + a c a b c = a b c
using the second equality we will have:
2 a b c = a b + b c + c a
And using the substitution method we can replace a by 1 ( b + c ) then we have:
2 b c ( 1 ( b + c ) ) = ( 1 ( b + c ) ) ( b + c ) + b c
2 b c 2 b 2 c 2 b c 2 = b + c b 2 c 2 2 b c + b c
2 b 2 c + 2 b c 2 + b + c b 2 c 2 3 b c = 0 s . t . 0 b , c 1
Zeihergp

Zeihergp

Beginner2022-05-29Added 6 answers

From ( 1 a ) ( 1 b ) ( 1 c ) = a b c you cannot deduce ( 1 a ) = 1 and so on. One set of solutions is to make both sides zero-let a = 1 , b = 0 , c = 0 or any permutation. The symmetry means that any permutation of a solution will also be a solution. Given one cubic and one linear equation you expect three solutions and we have that many.

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