If the difference of the square of a number and 3 times the number is 40 what is the number----Translation and Solution:

Answer 1

x^2 -3x = 40

x^2 -3x -40 = 0

(x-8)(x+5) = 0

x = 8 or -5

or

3x - x^2 = 40

x^2 -3x + 40 = 0

but x = 3/2 + (1/2)sqr(9-4(40)) has no real solution, just two imaginary solutions

the discriminant < 0. square root of a negative number is imaginary