The sum of two numbers is 7 and the difference of their reciprocal is 1 12 . What are the two numbers?

Let the first number be x so the other number is 7 - x According to the question, 1 x - 1 7 - x = 1 12 ⇒ 7 - x - x x 7 - x = 1 12 ⇒ 84 - 24 x = 7 x - x 2 ⇒ x 2 - 7 x - 24 x + 84 = 0 ⇒ x 2 - 31 x + 84 = 0 By using quadratic formula, we get x = - - 31 ± - 31 2 - 4 × 1 × 84 2 × 1 ⇒ x = 31 ± 961 - 336 2 ⇒ x = 31 ± 25 2 ⇒ x = 31 + 25 2 = 28 Or, x = 31 - 25 2 = 3 So, if one number is 28 , then the other number is 7 - 28 = - 21 . Or, if one number is 3 , then the other number is 7 - 3 = 4 .

The sum of two numbers is 7 and the difference of their reciprocal is 1 12 . What are the two numbers?

Let the first number be x so the other number is 7 - x According to the question, 1 x - 1 7 - x = 1 12 ⇒ 7 - x - x x 7 - x = 1 12 ⇒ 84 - 24 x = 7 x - x 2 ⇒ x 2 - 7 x - 24 x + 84 = 0 ⇒ x 2 - 31 x + 84 = 0 By using quadratic formula, we get x = - - 31 ± - 31 2 - 4 × 1 × 84 2 × 1 ⇒ x = 31 ± 961 - 336 2 ⇒ x = 31 ± 25 2 ⇒ x = 31 + 25 2 = 28 Or, x = 31 - 25 2 = 3 So, if one number is 28 , then the other number is 7 - 28 = - 21 . Or, if one number is 3 , then the other number is 7 - 3 = 4 .