Question

I have a number in my mind. When I put that number for x in 5x-x^2+3,I get - 4.which number do I have in my mind? Please answer fast

Answer 1

Answer:

(5+√21)/2

Step-by-step explanation:

5x - x^2 + 3 = 4

x^2 -5x +4-3 = 0

x^2 -5x + 1 = 0

x^2 - 5x + 25/4 - 25/4 +1 = 0

(x -(5/2))^2 = (25/4)-1

x- 5/2 = sqrt(21/4)

x = 5/2 + sqrt(21)/2

x = (1/2)( 5 + sqrt(21) )