4*(-2)^2 - 5*(-2)^3 = 4*4 -5(-8) = 16+40=56
2*(1-sin^2 (πx/3))+5sin(πx/3)=4; -2sin^2(πx/3)+5sin(πx/3)-2=0
t=sin(πx/3); -2t+5t-2=0; D=25-4*(-2)*(-2)=9=3^2' t1=(-5-3)/(-4)=2;
t2=(-5+3)/(-4)=0,5
sin(πx/3)=0,5 ili sin(πx/3)=2
πx/3=(-1)^n (π/6)+πn решений нет
х=(-1)^n (π/6 * 3/π)+π*(3/π)*n
x=(-1)^n (0,5)+3n, n-celoe
Решение
a₆ = 5 a₅ = 21
a₆ = a₅ + d
d = a₆ - a₅ = 5 - 21 = - 16
a₅ = a₁ - 16*4
a₁ = a₅ + 64 = 21 + 64 = 85
a₁₀ = a₁ + 9d = 85 - 9*16 = - 59
Sn = (a₁ + a₁₀)*10 / 2 = (85 - 59)*5 = 130