中等MATH-INEQ-009
Solve (x − 1)(x + 4) ≥ 0.
A. x ≤ −4 or x ≥ 1✓ 答案
B. −4 ≤ x ≤ 1
C. x < −4 or x > 1
D. x ≥ −4
解說
The product of two factors is non-negative outside the roots, and the weak inequality includes the roots. So x ≤ −4 or x ≥ 1. Between the roots the product is negative.