Решение :
n = ( an - a1 )/d + 1; n = ( 400 - 9 )/9 + 1 = 44;a44 = a1 + d * 43;a44 = 9 + 9 * 43 = 396;S44 = 0,5 * ( 2 * a1 + d * ( n - 1))* n;S44 = 0,5 * ( 18 + 9 * 43 ) * 44;S44 = 8.910.
64x³ - 16x² + x = 0
x(64x² - 16x + 1) = 0
x₁ = 0
64x² - 16x + 1 = 0
D = (- 16)² - 4 * 64 * 1 = 256 - 256 = 0
1) x=3; y=7; 7=9-2; 7=7; да;
2)x=-1; y=-6; -6=-3-2; -6=-5 нет;
3)x=0,2; y=-1,4; -1,4=0,6-2; -1,4=-1,4; да;