The number of distinct real roots of the equation |x||x + 2| - 5|x + 1| - 1 = 0 is .
Answer
3
Solution
The moduli change sign at x = -2, -1, 0, so solve in each interval and keep only roots lying in it.
x 0: x2 + 2x - 5x - 5 - 1 = 0 x2 - 3x - 6 = 0 x = 3 + 332 (one root)
-1 x < 0: -x2 - 2x - 5x - 5 - 1 = 0 (x + 6)(x + 1) = 0 x = -1 (one root)
-2 x < -1: -x2 - 2x + 5x + 5 - 1 = 0 (x - 4)(x + 1) = 0, no root in this interval
x < -2: x2 + 2x + 5x + 5 - 1 = 0 x2 + 7x + 4 = 0 x = -7 - 332 (one root)
Hence the equation has 3 distinct real roots.
Answer: 3