Question

in elimination method how we can understand where to use sum and where to use minus ..?any one can

Answer 1

you have to choose whether to cancel the x or y. for example
x + y = 2
x - y = 4
you can cancel y easily.
or u can cancel x by multiplying -
hope u understood

Answer 2

Heyaaa frnd..

The answer can be explained as

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The easiest method of all is the Elimination method.. You can very easily find ways to solve a equation using Elimination method..

Now, Coming to your question,

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Where to use Subtraction ??

Let's consider that there are two equations

4 x + 3 y = 10

3 x + 4 y = 20

In the given equations.. We find that the signs are almost equal... That is.. All are positive.. So We have to use Subtraction here..

Hope.. you know the rules for subtraction..

We have to change the signs of the equations and then cancel them.. Before that.. Let's make the coefficient of x or y equal..

Eqn 1 × 3 => 12 x + 9 y = 40

Eqn 2 × 4 => 12 x + 16 y = 80
_______________
- 7 y = - 40

Therefore.. It goes like that..

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Where to use Addition ??

We have to use Addition in the case where the signs are different..

For instance,

x - y = 10

x + y = 20

Here, the signs before 'y' is different in both the equations.. Therefore.. We can add these equations..

x - y = 10

x + y = 20
________
2x = 30

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Hope it helps ...

And here CutieBarbie :)