The number of real solutions of the equation x|x + 5| + 2|x + 7| - 2 = 0 is .
Answer
3
Solution
Case 1, x -5: x(x + 5) + 2(x + 7) - 2 = 0 x2 + 7x + 12 = 0 x = -3, -4 (both valid)
Case 2, -7 x < -5: -x(x + 5) + 2(x + 7) - 2 = 0 x2 + 3x - 12 = 0 x = -3 572
only x = -3 - 572 -5.27 lies in [-7, -5)
Case 3, x < -7: -x(x + 5) - 2(x + 7) - 2 = 0 x2 + 7x + 16 = 0, D = 49 - 64 < 0 (no root)
number of real solutions = 2 + 1 = 3
Answer: 3