(a+b) ³ = a ³ + 3×a²×b + 3×a×b² + b³ .
(a-b) ³ = a ³ - 3×a²×b + 3×a×b² - b³ .
(2а-1)³-8а³+5
1) (2а-1)³=(2а)³-3*(2а)²*1+3*2а*1²-1³;
(2а)³-3*(2а)²*1+3*2а*1²-1³-(2а)³+5=
=12а²+6а-1+5=
=12а²+6а+4
а=-2
=48-12+4=40
2)(0,5b-2)³-(0.5b+2)³
b=-2
(-1-2)³-(-1+2)³=
=(-1)³-3*(-1)²*2+ 3*(-1)*(2)²- (2)³ - (-1)³+3*(-1)²*2+ 3*(-1)*(2)² +(2)³=
= -15 -11=-26
3)(3x-4)³+(3x-2)³-27x³=
=(3x)³ -3*(3x)²*4 + 3*(3x)*(4)²- (4)³ + (3x)³ -3*(3x)²*2 + 3*(3x)*(2)²- (2)³-(3x)³=
=(3x)³-(4)³-(2)³ +3*[- (3x)²*4+3x*4²-(3x)²*2+(3x)*2²]=
27x³-72+3[-18x²+60x]=
=27x³-72-54x²+180x=
x=0.5
=27*(0.5)³-54*(0.5)²+180*0.5-72=
=3.375-13.5+90-72=
=7.875
я не можу зробити 4 номер, вибач