Question

y^2 + 4 Y - 21 factorise​

Answer 1

Answer:

y² + 4y - 21

y² + (7 - 3)y - 21

y² + 7y - 3y - 21

y(y+7) - 3(y+7)

(y+7) (y - 3)

Step-by-step explanation:

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Answer 2

Answer:

$(y-3)(y+7)$

Step-by-step explanation:

$=y^{2}+4y-21\\=y^{2}+7y-3y-21\\ =y(y+7)-3(y+7)\\=(y-3)(y+7)$

Product = -21 and Sum=+4, therefore factors = +7 and -3

$7-3=+4\\7*-3=-21$