Write and solve an inequality that describes that the height of the arch when it is greater than 52.
About 55 m from the left pylon to about 447 m from the left pylon.
Practice makes perfect
Let's consider the given function.
y=-0.00211x2+1.06x
The y-variable describes the height in meters ofthearchabovethewater.
We want to find the values of x for which the arch of the bridge is above the road. From the picture, we can see that the bridge is 52 meters above the water. Therefore, we want to find values of x such that y>52. Let's find them!
Now we can calculate the first root using the positive sign and the second root using the negative sign.
x≈-0.00422-1.06±0.82748
x≈-0.00422-1.06+0.82748
x≈-0.00422-1.06−0.82748
x≈55
x≈447
Step 2
The solutions of the related equation are approximately 55 and 447. Let's plot them on a number line. Since the original one is a strict inequality, the points will be open.
Step 3
Finally, we must test a value from each interval to see if it satisfies the original inequality. Let's choose a value from the first interval, x<55. For simplicity, we will choose x=0.
Since x=0 produced a false statement, the interval x<55 is not part of the solution. Similarly, we can test the other two intervals.
Interval
Test Value
Statement
Is it part of the solution?
55<x<447
100
32.9>0✓
Yes
x>447
500
-49.5≯0×
No
We can now write the solution set.
55<x<447
Since the x-variable represents the distance in meters from the left pylon, the arch is above the road about 55 m from the left pylon to about 447 m from the left pylon.
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