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# Simultaneous equations - PowerPoint PPT Presentation

Simultaneous equations. Yes, I know we’ve done this but you were a little ropey last week. 4 ways of solving them. Pros If you guess well, then easy to solve. Cons Hard to show your working. Only works for really simple ones. Can take a lot of time. 1 Guessing the answers. Pros

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Simultaneous equations

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## Simultaneous equations

Yes, I know we’ve done this but you were a little ropey last week.

### 4 ways of solving them

Pros

If you guess well, then easy to solve.

Cons

Only works for really simple ones.

Can take a lot of time.

Pros

Works for all but the most complicated equations( A – level).

Cons

Need to show all working and work carefully.

May need to multiply equations first

Pros

Will work every time

Works for families of equations

Cons

Not always accurate

Time consuming

Long-winded, lots of room for mistakes to creep in.

### 3 Graphically

Pros

Can be quickest way

Best way for complicated equations e.g.. powers

Cons

Not suitable for all equations

More likely you are looking at A – level paper.

### 2x + 2y = 83x – y = 16

Number equations

2x + 2y = 8

3x – y = 16

Make ‘y’s the same by multiplying

x 2 6x – 2y = 32

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### 2x + 2y = 83x – y = 16

2x + 2y = 8 Same no. of y’s in

3x – y = 16

6x – 2y = 32

+ 8x = 40

x = 5

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### 2x + 2y = 83x – y = 16

2x + 2y = 8

3x – y = 16

Substitute x = 5 in (easiest)

2 x 5 + 2y = 8

10 + 2y = 8

2y = -2

y = -1

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### 2x + 2y = 83x – y = 16

We have x = 5 and y = -1 so now we

CHECK IT

Check inbecause we haven’t used that yet

(3 x 5) – (-1) = 15 - - 1

= 15 + 1

= 16

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