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Algebra/Systems of Equations

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Expert: - 12/28/2005


Question
Which expression can be substituted for x in the top   equation of the sytstem below to solve the sytem by subsitution.

2x=10y=1
x-4y=-4

Answer
Hello Sofia,

If we take the 2nd equation and solve for x, we get
x=4y-4...then substitute that into the 1st equation:
2(4y-4)-10y=1 (I gather you meant "2x-10y" not "2x=10y").
Expanding: 8y-8-10y=1 ==> -2y-8=1 ==> -2y=9
so y=-9/2=-4.5...then x=-22

OK?

Abe

Algebra

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Volunteer

Abe Mantell

Expertise

Hello, I am a college professor of mathematics and regularly teach all levels from elementary mathematics through differential equations, and would be happy to assist anyone with such questions!

Experience

Over 15 years teaching at the college level.

Organizations
NCTM, NYSMATYC, AMATYC, MAA, NYSUT, AFT.

Education/Credentials
B.S. in Mathematics from Rensselaer Polytechnic Institute
M.S. (and A.B.D.) in Applied Mathematics from SUNY @ Stony Brook

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