The number of parts per million of nitric oxide emissions y from a certain car engine is
approximated by the model
y = −5.05x^3+ 3865x − 38531.2 , 13 ≤ x ≤ 18 ,
where x is the air-fuel ratio.
It is observed from the graph that two airfuel ratios produce 2400 parts per million of
nitric oxide, with one being 15.
Find the other.

Question

The number of parts per million of nitric oxide emissions y from a certain car engine is
approximated by the model
y = −5.05x^3+ 3865x − 38531.2 , 13 ≤ x ≤ 18 ,
where x is the air-fuel ratio.
It is observed from the graph that two airfuel ratios produce 2400 parts per million of
nitric oxide, with one being 15.
Find the other.

mertsj · Answer

$$-5.05x^3+3865x-38531.2=2400$$
$$-5.05x^3+3865x-36131.2=0$$

mertsj · Answer

We know that one root is 15 so let's divide by x-15

mertsj · Answer

Is that supposed to be x^2 instead if x^3?