CBSE Class 8CBSE
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Addition and Subtraction of Algebraic Expressions

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notes

For example, to add  `7x^2 – 4x + 5` and 9x – 10, we do
`7x^2 – 4x + 5`
+         9x – 10
_________________ 
`7x^2 + 5x – 5`

Observe how we do the addition. We write each expression to be added in a separate row. While doing so we write like terms one below the other, and add them, as shown. 

Note :  subtraction of a number is the same as addition of its additive inverse. Thus subtracting –3 is the same as adding +3. Similarly, subtracting 6y is the same as adding – 6y; subtracting – 4y2 is the same as adding 4y2 and so on. The signs in the third row written below each term in the second row help us in knowing which operation has to be performed.

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