FP1 Simultaneous Equation Question Please Help!

I think this question should be quite straight forward but I am stuck on question 2(e), Exercise 1A in the ocr textbook. It is a simultaneous equation with 3 variables and 3 equations, however, unlike the other questions in the exercise only 2 of the 3 variables are present in each equation so I am stuck on how to solve it.
The equations are:
y + z = 4
x + y = 5
x + z = 3
Would greatly appreciate some help! Thank you.

The book advices you to solve it as shown in the example below:

Reply 1

Student 977

2

You need to start by subtracting two of the equations. Maybe do

x+y=5 minus x+z=3

Reply 2

giantbecky

OP

8

Original post by Student 977

You need to start by subtracting two of the equations. Maybe do

x+y=5 minus x+z=3

Ahh I see thank you very much!

I think I thought that for this method to work, you had to always find z first... but I guess not?

I think I am just a bit confused by this method - it seems a bit unnecessary? Do you know if the order of the equations actually matters? Since in the example it talks about swapping the order so there is always x in the first equation etc., but surely this doesn't really matter!?

Thank you again!

Reply 3

Student 977

2

What you need are two equations which have the same two variables in. The only way to do this is to subtract two of the equations. You can then solve the two equations with the same variable in simultaneously (e.g., by rearranging and substituting). It doesn't matter which two equations you subtract since they all share a variable with another. I just find it easier to choose a subtraction that is going to give you a positive number (because I like to make it easy!).

Reply 4

giantbecky

OP

8

Original post by Student 977

What you need are two equations which have the same two variables in. The only way to do this is to subtract two of the equations. You can then solve the two equations with the same variable in simultaneously (e.g., by rearranging and substituting). It doesn't matter which two equations you subtract since they all share a variable with another. I just find it easier to choose a subtraction that is going to give you a positive number (because I like to make it easy!).

Ahhh yes I see what you mean! I think I was overcomplicating it in my head as I think that the steps that the book shows are unnecessary... but I expect that's to help when it gets much harder!

Thank you very much for your help!! :smile:

FP1 Simultaneous Equation Question Please Help!

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