Найдите восьмой член арифметической прогрессии, если а7+а9=0, 18. напишите подробно

A7+a9=a1+6d+a1+8d=2a1+14a=2(a1+7d)=2*a8=0.18 a8=0.09

1) 2x - 2 = 0 2x = 2 x = 2/2 x = 1 2) 4x² + x - 5 = 0 d = b² - 4ac = 1² - 4 × 4 × ( - 5) = 1 + 80 = 81 = 9² x₁ = (- 1 + 9)/ 8 =1 x₂ (-1 - 9)/8= - 10/8 = -1,25 3) (x- 6)(x - 6) = 7 - x x² - 12x + 36 - 7 + x =0 x² - 11x + 29 = 0 d = b² - 4ac = (-11)² - 4 × 1 × 29 = 121 - 116 = 5 x₁,₂ = 11⁺/⁻√5 / 2 4) x- 36 + 4x = 3x + 2 5x - 3x = 36 + 2 2x = 38 x = 38/2 x = 19 5) - 5x - 9 + 18x = 9x - 1 13x - 9x = 9 - 1 4x = 8 x = 8/4 x = 2 6) 4x² + 6x - 2 = (x - 1)(x - 1) 4x² + 6x - 2 = x² - 2x + 1 4x² + 6x - 2 - x² + 2x - 1 = 0 3x² + 8x - 3 = 0 d = b² - 4ac = 8² - 4 × 3 × (-3) = 64 + 36 = 100 = 10² x₁ = (- 8 + 10 )/ 6 =2/6 = 1/3 x₂ = (-8 - 10) / 6 = - 18/6 = - 3 7) 2x² + 11x + 34 = ( x + 6)(x + 6) 2x² + 11x + 34 = x² + 12x + 36 2x² + 11x + 34 - x² - 12x - 36 = 0 x² - x - 2 = 0 d = b² - 4ac = (-1)² - 4 × 1 × ( - 2) = 1 + 8 =9 = 3² x₁ = (1 + 3) / 2 = 2 x₂ = (1 - 3) / 2 = - 2/2 = - 1

5а-10b=18 5(a-2b) = 18 a-2b = 18/5 a-2b =3.6 a)   7.2   = 7.2   =   2     a-2b       3.6 б) 4b - 2a = -2(a -2b)   = - 2*3.6 = -2.4           3             3                     3 в)   a² - 4b²       = (a-2b)(a+2b)   = a-2b   = 3.6 = 4     0.9a+1.8b         0.9(a+2b)           0.9       0.9