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What is the solution of (x+8)/(5x+-1)>0?

User Blachniet
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1 Answer

15 votes
15 votes

Answer:

the solution set is (-infinity, -8) ∪ (-8, 1/5)

Explanation:

x + 8 changes sign at x = -8.

I'll assume you meant 5x - 1 (as 5x+- is meaningless). 5x - 1 changes sign at x = 1/5.

Subdivide the x-axis using the two x-values found above:

(negative infinity, -8), (-8, 1/5), (1/5, infinity.

Choose a representative value from each interval. I'm choosing x = -10, x = 0 and x = 1.

Now test the given inequality at each of these x-values. Is the result true or false?

x + 8

---------- > 0

5x - 1

For x = -10:

-10 + 8

--------------- > 0 => -2/(-51) => 2/51 This is TRUE

5(-10) - 1

For x = 1:

1 + 8

---------- > 0 => 9/4 This is TRUE

5 - 1

For x = 0:

8

---------- > 0 This is FALSE

- 1

Therefore the solution set is (-infinity, -8) ∪ (-8, 1/5)

User George Walters II
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