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# 中一maths (find mistakes)

find mistakes

(x+y)二次方=x二次方*y二次方

一. 2*[(2a)*(3b)]=2*(2a)*2*(3b)

二. Peter claims that when a number x is increased by 10% and then decreased by 10%, the value of x is unchanged.

His calculation: x( 1 + 10% - 10%) = x

Peter is wrong. Point out the mistake.

Update:

三. what can be multiplied to x - 2 give a product containing the term -3x二次方? Find the polynomial.

### 1 Answer

Rating

- kigrstarLv 41 decade agoFavorite Answer
find mistakes

1) (x+y)二次方=x二次方*y二次方

(x+y)^2 = x^2 + y^2

(x^2) (y^2) = x^2．y^2

∴(x+y)^2 = (x^2) (y^2) is wrong.

2) 2*[(2a)*(3b)]=2*(2a)*2*(3b)

2[ (2a)(3b) ]

=2(6ab)

=12ab

2(2a)．2(3b)

=4a．6b

=24ab

∴2 [ (2a)(3b) ] = 2(2a)．2(3b) is wrong.

3)

The calculation is:

x(1+10%)(1-10%)

=110%．90% x

=99%x

Source(s): me`

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