Given that x=−4 is a root of x132x231x=0
Expanding the determinant using the first row:
xx21x−2131x+313x2=0
Computing each 2×2 determinant:
x21x=x2−2
131x=x−3
13x2=2−3x
Substituting back:
x(x2−2)−2(x−3)+3(2−3x)=0
x3−2x−2x+6+6−9x=0
x3−13x+12=0
For a cubic equation x3+bx2+cx+d=0, the sum of all roots equals −b.
The equation is: x3+0x2−13x+12=0
Sum of all three roots =−0=0
Given one root is x=−4:
(−4)+(sum of other two roots)=0
Sum of other two roots =4