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

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  • 1 decade ago
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    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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