Question
Question: If the sum of two of the roots of x<sup>3</sup> + px<sup>2</sup> + qx + r = 0 is zero, then pq =...
If the sum of two of the roots of x3 + px2 + qx + r = 0 is zero, then pq =
A
– r
B
r
C
2r
D
– 2r
Answer
r
Explanation
Solution
a + b + g = – p Let a + b = 0 Ž g = – p
Ž – p is root of x3+ px2 + qx + r = 0
– p3 + p3 – pq + r = 0 Ž pq = r