Math Is Fun Forum

Jamesbob

Member

Registered: 2007-03-12

Posts: 2

solving the following

I have a few questions i hope somebody can help me with, these are the last three I need so help is really appreciated.

1) 7x - 3y = 0
    5x = 6 + 3y

2) 4x - 5y = 7
    12x - 3 = 9y

3) x = 2y + 1
    3x - 4y = 7

thank you!

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: solving the following

With this type of question, you need to combine the two equations to eliminate one of the unknowns. Then you're just left with one equation and one variable, which should be easily solvable.

All of these have the same method, so if I do one then you should be able to do the other 2.

1)
7x - 3y = 0
5x = 6 + 3y     -->   6 + 3y = 5x

Adding these two equations gives 7x + 6 = 5x, because the y terms cancel.
This simplifies to 2x + 6 = 0, which solves to give x = -3.

The other two can be solved in much the same way, except that you may have to multiply one of the equations through by a constant first.

For example, in 2) you could multiply everything in the first equation by 3 to get a 12x in both of them. After that, you solve in exactly the same way.

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Why did the vector cross the road?
It wanted to be normal.

Jamesbob

Member

Registered: 2007-03-12

Posts: 2

Re: solving the following

thank you !