To solve this, we first find the roots of the equation X2−2X−8=0 using the quadratic formula X=2a−b±b2−4ac, where a=1,b=−2,c=−8
step 3
Calculating the discriminant: b2−4ac=(−2)2−4(1)(−8)=4+32=36. Thus, the roots are X=22±6
step 4
This gives us the roots X=4 and X=−2
step 5
We can now test intervals around the roots: (−∞,−2), (−2,4), and (4,∞) to determine where the inequality holds
step 6
Testing X=−3 in (−∞,−2): (−3)2−2(−3)−8=9+6−8=7≥0 (true)
step 7
Testing X=0 in (−2,4): 02−2(0)−8=−8≥0 (false)
step 8
Testing X=5 in (4,∞): 52−2(5)−8=25−10−8=7≥0 (true)
step 9
Therefore, the solution set is X≤−2 or X≥4
Answer
The solution set is (−∞,−2]∪[4,∞)
Key Concept
Solving quadratic inequalities involves finding the roots and testing intervals.
Explanation
The solution set includes values of X that satisfy the inequality X2−2X−8≥0. The roots divide the number line into intervals, which we test to find where the inequality holds true.
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