(m²-2m)²-1 = (m² - 2m - 1)(m²-2m+1)
16-(m² +4m)² = 4^2 -(m² +4m) = (4 - m²- 4m)(4 + m² + 4m)
Cos(п/12)*cos(7п/12)-sin(п/12)*sin(7п/12)=cos((п/12)+(7п/12))=cos(3п/4)=-√(2)/2.
a₁ = -21
d = 3
S₂₀ = (2a₁ + d(n-1))*n/2 = (-42+3*19)*10 = 150
X=yabloni
y=grushi
z=slivy
x+y+z=130
3y=x y+10=z
Togda poluchitsa x+y+z= 3y + y + y+10=130
5y+10=130
5y=120
(Grushi)y=24
(Yabloki)x=3y=72 (Slivy)z=y+10=34