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January 30, 2015

January 30, 2015

Posted by **chrissy** on Sunday, September 13, 2009 at 7:46pm.

Let a, b, and c be real numbers such that a-7b+8c=4 and 8a+4b-c=7. Then a^2-b^2+c^2= ?

can someone please help?! i don't know what method to use to solve this or where to start

- mathhh! -
**MathMate**, Sunday, September 13, 2009 at 8:38pmWhat you'd like to do is to solve the simultaneous equations

a-7b+8c=4

8a+4b-c=7

for a and b in terms of c.

Substitute the values of a and b in the expression a²+b²+c² and wait for the magic to happen.

If you do your math correctly, magic will happen.

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