The number of distinct real roots of the equation |x + 1||x + 3| - 4|x + 2| + 5 = 0, is
Answer
2
Solution
Critical points: x = -3, -2, -1
[figure]
x -3: (x + 1)(x + 3) + 4(x + 2) + 5 = 0 (x + 4)2 = 0 x = -4 (accepted)
-3 < x -2: -(x + 1)(x + 3) + 4(x + 2) + 5 = 0 x2 = 10 (rejected, 10 not in interval)
-2 < x < -1: -(x + 1)(x + 3) - 4(x + 2) + 5 = 0 x2 + 8x + 6 = 0
x = -4 10 -0.84, -7.16 (rejected, not in interval)
x -1: (x + 1)(x + 3) - 4(x + 2) + 5 = 0 x2 = 0 x = 0 (accepted)
∴ the distinct real roots are -4 and 0, i.e. 2 roots
Answer: 2