Question

Write a quadratic formula or expression for this:

The product of a certain whole number and four more than that number is 140, write a quadratic expression / formula and find the number. ​

Answer 1

number is 10

Explanation:

let n be the number, then 4 more than the number is n + 4, thus

n(n + 4) = 140 , that is

n² + 4n = 140 ( subtract 140 from both sides )

n² + 4n - 140 = 0

Consider the factors of the constant term (- 140) which sum to give the coefficient of the n- term (+ 4)

The factors are + 14 and - 10 , since

14 × - 10 = - 140 and 14 - 10 = + 4 , thus

(n + 14)(n - 10) = 0 ← in factored form

Equate each factor to zero and solve for n

n + 14 = 0 ⇒ n = - 14

n - 10 = 0 ⇒ n = 10

Since n is a whole number the the required number is 10