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geatkins
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Foundations Page 82

by geatkins Fri May 07, 2010 9:13 pm

at the top of the page it says:

(J + 8) = 2(B + 8) --> J + 8 = 2B + 16
J = B + 13 --> J - 13 = B

It seems like the second line above should be:

J = 2B + 8

I am having a brain fart. What am I missing here? Can somebody please walk me through this problem?

Thanks in advance for any help.

Glenn Atkins
mschwrtz
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Re: Foundations Page 82

by mschwrtz Fri Jun 04, 2010 3:04 am

Good question. The reason you can't see how to infer J = B + 13 from J + 8 = 2B + 16 is that it's impossible to do so. But the text doesn't draw that inference either.

Look back to p. 80-81. Remember that this problem included two equations, (J + 8) = 2(B + 8) AND J = B + 13.

On page 82, after the text rewrites the first of those equations as J + 8 = 2B + 16, it reintroduces the second of those equations. This allows you to use one equation to solve for B in terms of J, and then to plug that expression in terms of J into the other equation.


The line that reads "J = B + 13 --> J - 13 = B" is not a reworking of the line immediately above it. Rather, it is a reintroduction of the equation from the previous page.
geatkins
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Re: Foundations Page 82

by geatkins Fri Jun 04, 2010 9:02 am

And the light comes on. Thanks.

Glenn
mschwrtz
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Re: Foundations Page 82

by mschwrtz Fri Jun 04, 2010 1:50 pm

You're welcome. Glad to help.