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jolaisa's Question
Math
Posted 4 months ago
Find The Solution set of X²-2X-8≥0
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Answer from Sia
Verified answer
Posted 4 months ago
Solution by Steps
step 1
We start with the inequality X22X80 X^2 - 2X - 8 \geq 0
step 2
To solve this, we first find the roots of the equation X22X8=0 X^2 - 2X - 8 = 0 using the quadratic formula X=b±b24ac2a X = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} , where a=1,b=2,c=8 a = 1, b = -2, c = -8
step 3
Calculating the discriminant: b24ac=(2)24(1)(8)=4+32=36 b^2 - 4ac = (-2)^2 - 4(1)(-8) = 4 + 32 = 36 . Thus, the roots are X=2±62 X = \frac{2 \pm 6}{2}
step 4
This gives us the roots X=4 X = 4 and X=2 X = -2
step 5
We can now test intervals around the roots: (,2) (-\infty, -2) , (2,4) (-2, 4) , and (4,) (4, \infty) to determine where the inequality holds
step 6
Testing X=3 X = -3 in (,2) (-\infty, -2) : (3)22(3)8=9+68=70 (-3)^2 - 2(-3) - 8 = 9 + 6 - 8 = 7 \geq 0 (true)
step 7
Testing X=0 X = 0 in (2,4) (-2, 4) : 022(0)8=80 0^2 - 2(0) - 8 = -8 \geq 0 (false)
step 8
Testing X=5 X = 5 in (4,) (4, \infty) : 522(5)8=25108=70 5^2 - 2(5) - 8 = 25 - 10 - 8 = 7 \geq 0 (true)
step 9
Therefore, the solution set is X2 X \leq -2 or X4 X \geq 4
Answer
The solution set is (,2][4,) (-\infty, -2] \cup [4, \infty)
Key Concept
Solving quadratic inequalities involves finding the roots and testing intervals.
Explanation
The solution set includes values of X X that satisfy the inequality X22X80 X^2 - 2X - 8 \geq 0 . The roots divide the number line into intervals, which we test to find where the inequality holds true.

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