Tip:A–D to answerE for explanationV for videoS to reveal answer
If the roots of the equation x2+4x+a2−3a=0 are real then the value of a is (are)
- A.
a∈(−∞,−1)∪(4,∞)
- B.
a∈(−∞,−1]∪[4,∞)
- C.
α∈[−2,4]
Explanation
x2+4x+α2−3α=0
Roots real
D≥0
D=(4)2−4(1×(α2−3α))≥0
16−4(α2−3α)≥0
4−(α2−3α)≥0
−(α2−3α)≥−4
−α(α−3)≥−4
α=+4,−1
α∈[−1,4]
Explanation
x2+4x+α2−3α=0
Roots real
D≥0
D=(4)2−4(1×(α2−3α))≥0
16−4(α2−3α)≥0
4−(α2−3α)≥0
−(α2−3α)≥−4
−α(α−3)≥−4
α=+4,−1
α∈[−1,4]