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№1

а) 2x (x-3) - 3x (x+5)

б) (a+7) (a-1) + (a-3)

в) 3 (у+5) ^2-3y^2

№2

а) c^3-16c

б) 3a^2-6ab+3b^2

№3

а) 81a^4-1

б) y^2-x^2-6x-9

1) 2x (x-3) - 3x (x+5) = 2xˇ2-6x-3xˇ2-15x=-xˇ2-21x

(a+7) (a-1) + (a-3) = aˇ2+7a-a - 7+a-3=aˇ2+6a-10

3. (y+5) ˇ2-3yˇ2=3yˇ2+30y+75-3yˇ2=30y+75

2) cˇ3-16c=c (cˇ2-16) = c (c+4) (c-4)

3aˇ2-6ab+3bˇ2=3 (aˇ2-2ab+bˇ2=3 (a-b) ˇ2

3) 81aˇ4-1 = (9aˇ2) ˇ2 - 1ˇ2 = (9aˇ2+1) (9aˇ2-1) = (9aˇ2+1) (3a+1) (3a-1)

yˇ2-xˇ2-6x-9=yˇ2 - (xˇ2+6x+9) = yˇ2 - (x+3) ˇ2=

= (y+x+3) (y-x-3)