Can you explain Fig? Why C
(-a,0) and (-b,0) represent the 2 points that intersect the X-axis.
Actually, we have 2 unknow roots / variables. So we need 2 different equations, defining 2 relationships between a and b, to determine the values of a & b.
So, combining (1) with (2)
Equation 1 = Statment 1 : a + b = -1
Equation 2 from expliciting y= x^2 + (a+b)*x + a*b
-6= 0^2 + (a+b)*0 + a*b
<=> a*b = -6
Kind of symetrical equations.
a^2 + a - 6 = 0 => a=-3 or a=2 thus b=-3 or b=2.... We have the 2 points