Question

x la a doua -x-20 =0

Answer 1

Delta=b patrat -4ac
Delta= Radical din 81
Delta=9
X1=1+9/2
X1=5
X2=1-9/2
X2=-4

Answer 2

x² -x - 20 = 0 => x² - x = 20 => x·(x-1) = 20 

→ 5·4 = 20 => 5·(5-1) = 20 => x = 5
→ -5·(-4) = 20 => -4·(-5) = 20 => -4·(-4-1) = 20 => x = -4

=> S = {-4, 5}