Unknown values
We need to find a number x
We know its square (x²) decreased by 3 times it (3x) is 28. Then
x² - 3x = 28
x² - 3x - 28 = 0 [Simplifying the equation]
Since - 7 + 4 = - 3 and (-7) (4) = - 28, we factor the polynomial:
(x - 7)(x + 4) = 0 [Factoring the polynomial]
When a multiplication, like (x - 7)(x + 4), equals cero?
it equals cero if and only if
(x - 7) = 0 or (x + 4) = 0
Then, simplifying both equations
x = 7 or x = - 4
Answer: x = 7 or x = - 4