How to solve, when I have two equation.

When you have 2 equation like this↓

・X = 2Y+10

・2X + 3Y = 30

You can solve by 3 way.

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1.Eliminatin

I think this is easiest way to solve this question. When you use this way, you need to 3 things.

 

1.Change 2 or 1 equation to same coefficient.

・X = 2Y+10

・2X + 3Y = 30

For this question, you need to change by 2 times.

X×2 = (2Y+10)×2

→ 2X = 4Y + 20

 

2.Change form to aX + bY = C

・2X = 4Y + 20

・2X + 3Y = 30

↓

・2X – 4Y = 20

・2X + 3Y = 30

 

3.Just subtract.

2X – 4Y = 20

– )2X + 3Y = 30

——————-.

-7X = -10

→ X = 10/7