a(1) = -3
a(2) = -6
d = a(2)-a(1)
d = -6+3 = -3
a(25) = a(1) + 24d
a(25) = -3 + 24*(-3) = -75
Ctg²t·(cos²t-1)+1=ctg²t·(-(1-cos²t))+1=ctg²t·(-sin²t)+1=(cos²t/sin²t)·(-sin²t)+1=
=-cos²t+1=sin²t
4х²-9)(4х²+9)=16х⁴-81
2) (7r-8q)(7r+8q)
3) 4x²-12x+9-4x²+4x+8x+4=13