Math CentralQuandaries & Queries


Question from laura, a student:

ok! i really need help with this question plz help!!

x = - 4y +5
x+2y = 7

Hi Laura,

This problem is set up so that you can use the method of substitution directly. The first equation tell you an equivalent way to write x, it says that x is equivalent to -4 y + 5. Thus in the second equation, x + 2y = 7 you can replace x by this equivalent expression. Hence

x + 2y = 7

can be rewritten

-4y + 5 + 2y = 7.

Another way to describe this is to say that I substituted -4 y + 5 for x.

Now you have one equation in the variable that you can solve for y. Once you have a numerical value for y use x = -4 y + 5 to find a numerical value for x.

At this point you can check that your answer is correct. Substitute the values of x and y you found into the second equation, x + 2y = 7, and see if it results in a true statement.

If you need more helps write back,

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