х^2-х-5=0
1x2 - 1x - 5 = 0
D = b2 - 4ac = (-1)2 - 4∙1∙(-5) = 21
D > 0 ⇒ уравнение имеет 2 корня
x = -b ± √D / 2a
x1 = (1 - √21) / (2∙1) = -1.79128784748
x2 = (1 + √21) / (2∙1) = 2.79128784748
(1 - √21)³/8+(1+√21)³/8=(1-3√21+3√21²-√21³+1+3√21+3√21²+√21³)/8=(2+3*21+3*21)/8=128/8=16