Question

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Answer 1

Answer:

(3+y) (3-y) (9-y²)

3 + y × 3 - y × 9 - y²

3 + 3+ 9 + y - y - y²

15 - y²

Answer 2

Step-by-step explanation:

$(3 + y)(3 - y)(9 - {y}^{2} ) \\ = ( {3}^{2} - {y}^{2} )(9 - {y}^{2} ) \\ = (9 - {y}^{2} )(9 - {y}^{2} ) \\ = (9 - {y}^{2} )^{2} \\ ( {9}^{2} - 2 \times 9 \times {y}^{2} + ( {y}^{2} )^{2} ) \\ = 81 - 18 {y}^{2} + {y}^{4}$

$use \: \: the \: \: identity \\ \\ (x + y)(x - y) = ( {x}^{2} - {y}^{2} ) \\ \\ (x - y) ^{2} = {x}^{2} - 2xy + {y}^{2}$