math!

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My teacher said we are supossed to solve this using systems of equations:

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

  • math! -

    What 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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