⎩ ⎪ ⎪ ⎨ ⎪ ⎪ ⎧ x z = y 3 8 y z = x 3 2 z = 4 x + 4 y
There are two triplets ( x , y , z ) of solutions to this system of equations, one of which is ( 1 , 1 , 2 ) . If the other set is ( a , b , c ) , what is the value of b a × c rounded to three decimal places?
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why discard the negative y? for example (1, -1, 2) is also a solution
For the third equation, is one of the terms supposed to be y ? Otherwise, can we make it 2 4 x directly?
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Considering the third equation, x , y , z > 0 . ( 0 , 0 , 0 ) isn't a solution because 0 0 is not defined.
y z = x 3 2
y z × z = x 3 2 × z = ( x z ) 3 2 = ( y 3 8 ) 3 2 = y 9 1 6
y z 2 = y 9 1 6 This means that either y = 1 or z 2 = 9 1 6 . For y = 1 we get the first given set of solutions ( 1 , 1 , 2 ) .
For z 2 = 9 1 6 we get z = 3 4 , meaning c = 3 4 .
From the first equation, we get x 3 4 = y 3 8 , or x = y 2 .
From this point, we could solve for x and y, but that's unnecessary because we know that a = b 2 .
b a × c = b b 2 × 3 4 = b b × 3 4 = 1 × 3 4 = 3 4 = 1 . 3 3 3