x² - 14x + 7 = 0

a = 1; b = -14; c = 7

D = (-14)² - 4×7 = 196 - 28 = 168

x1,2 = (-b ± √D)/2a

x1,2 = (14 ± √168)/2 = 7 ± √42

x1 = 7 + √42

x2 = 7 - √42

1/x1 + 1/x2 = 1/(7 + √42) + 1/(7 - √42) = ((7 - √42)+(7 + √42))/(7² - (√42)²) = 14/7 = 2

Відповідь: 2