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LostInParadise's avatar

Ready for another test of mathematical intuition?

Asked by LostInParadise (31907points) April 30th, 2020
4 responses
“Great Question” (1points)

Given the equations:
x+y=a
x+z=b
y+z=c
where a, b and c are constants, we want to solve for x, y and z in terms of a, b and c.

It turns out that x=½(a+b-c)
Can you now use intuition without any algebraic manipulation to immediately give the values of y and z in terms of a, b and c?

It is all about symmetry. For example, do you see why a and b have the same coefficient in the expression for x? x is indifferent to y and z. The first equation has x and y and the second has an identical expression for x and z. From the point of view of x, a and b are equivalent. The third equation is y+z=c, which again from x’s point of view, fails to distinguish y from z, but provides different type of information from x’s viewpoint, from the first two equations.

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Answers

ragingloli's avatar

It is all 0.

LostInParadise's avatar

Here is a simpler example of how symmetry can be used.
x + 3y = a
3x + y = b

Given that x = 1/8(3b – a), it follows by the symmetry of the equations that we must have:
y = 1/8(3a – b). Do you see how this relates to the original problem?

LostInParadise's avatar

I see I am getting no takers, so here is the way to look at the original problem. I described how things look to x. They look pretty much the same to y. y is part of y+z=c and y+x=a and there is an additional equation of x+z=a that relates x and z.

Therefore we should expect to have y = ½(a + c – b) and z is set up the same way so we should have z = ½(b + c – a)

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