4x³-24x²-4x+120=4*(x³-6x²-x+30)
x³-6x²-x+30 |_ x+2_
x³+2x² | x²-8x+15
---------
-8x²-x
-8x²-16x
------------
15x+30
15x+30
----------
0
x²-8x+15=0 D=4
x=5 x=3 ⇒
4x³-24x²-4x+120=4*(x+2)*(x-3)*(x-5) ⇒
x+a=x-5
a=-5
Ответ: a=-5.
cos(π/7)+cos(π/15)= 2cos((π/7+π/15)/2)*cos((π/7-π/15)/2)= 2cos(11π/105)*cos(4π/105)
(3х-1)^2+(3х-1)*(3х+1)=(3х-1)^2+9х^2-1=(3х)^2-2*3х*1+1^2+9х^2-1=9х^2-2*3х+9х^2=18х^2-2*3х=18х^2-6х.