The correct option is C { 9,9 } #160; #160; y^2 81=0 = gt;y^2 9^2=0 = gt;(y+9)(y 9)=0 #160;[ a^2 b^2=(a+b)(a b) ] = ...

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Algebraic Identities

Solve for y...

Question

Solve for $y : y^{2} - 81 = 0$

{- 1, 1}

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{9}

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{- 9, 9}

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{81}

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Solution

The correct option is C ${- 9, 9}$
$y^{2} - 81 = 0$
$=> y^{2} - 9^{2} = 0$
$=> (y + 9) (y - 9) = 0$ [ $a^{2} - b^{2} = (a + b) (a - b)$ ]
$=> y + 9 = 0$ or $=> y - 9 = 0$
$=> y = - 9$ or $=> y = 9$

Thus {9,-9} is the soution

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