4(2а+1)²-(3а)²=(2(2а+1)-3а)) *(2(2а+1)+3а))=(4а+2-3а)(4а+2+3а)=(а+2)(5а+2)
1)a1=93 a2=89 d=89-93=-4
an=93-4(n-1)<0
93-4n+4<0
4n>97
n>24 1/4
n=25
2)x2+2x-15=0
x1+x2=-2 U x1*x2=-15
x1=-5 U x2=3
1) (a+3)^2 + (a-3)(a+3) + 6a = a^2 + 6a + 9 + a^2 - 3^2 +6a = 2a^2 + 12a
2) xy-2y=y(x-2)
16a^2 - 81 = 4^2a^2 - 9^2 = (4a-9)(4a+9)
3x^2 - 6x^3 = 3x^2(1-2x)
x^2-10x+25 = (x-5)^2
3(x-1) +y(x-1) = (x-1)(3+y)
2a^2 - 4ab + 2b^2 = 2(a-b)^2
3) a^2 - 3ab + 3a - 9b = a(a+3) - 3b(a+3) = (a+3)(a-3b) = (1 + 3)*[1-3*(-1/3)]=
= 4*[1 + 1] =8