9, a,

`a+b+c = 15` és `d=2`

`ad+bd+cd` = `(a+b+c)*d` = `15*2` = `ul("30")`

b,

`ab=ac=-3`

`a(b+c)` = `ab+ac` = `(-3)+(-3)` = `ul("-6")`

c,

`ac=ad=bc=bd=-2`

`(a+b)(c+d)` = `ac+ad+bc+bd` = `(-2)+(-2)+(-2)+(-2)` = `ul("-8")`


10,

`(3t-7)^2+(4t+9)(3t-7)` = `(3t-7)(3t-7)+(4t+9)(3t-7)` = `(3t-7)(3t-7+4t+9)` = `(3t-7)(7t+2)`

11, a,

`1+3/5 a+9/25 a^2+27/125 a^3` = `(1+3/5a)*(1+9/25a^2)`

b,

`(3x+1)^2-(3x+1)(3x+2)-6x(3x+1)` = `(3x+1)(3x+1-(3x+2)-6x)` = `(3x+1)(-6x-1)` = `-(3x+1)(6x+1)`