Answer:
║ x - 231 ║ ≤ 459
Step-by-step explanation:
Since we have 228 ft below sea level, this is x' = -228 ft. Also, we have 690 ft above sea level, this is x" = 690 ft.
Since x is our elevation in feet, x ranges from -228 ≤ x ≤ 690.
To write an absolute value equation for x, we first take the average of the two values for the ranges to obtain the ideal value of x.
So, ideal value = [690 + (-228)]/2 = 462/2 = 231.
We also find the tolerance by taking the difference of both values and dividing by 2. So tolerance = [690 - (-228)]/2 = [690 + 228)]/2 = 918/2 = 459.
Subtracting 231 from each value of the inequality we have
-228 - 231 ≤ x - 231 ≤ 690 - 231
-459 ≤ x - 231 ≤ 459
Since we have in magnitude the values on the left and right side of the inequality,
So ║ x - 231 ║ ≤ 459
