The point (4,y) has a known x coordinate of x = 4. The y coordinate is unknown right now so we'll just call it y.
Draw a vertical line (see side note below) through 4 on the x axis. I've done so in red (see attached image). The red line crosses the graph at the point (4,1) so this tells us that
y = 1Answer: y = 1
Side Note: you don't have to draw a vertical red line but it's handy to see how it works out. After you get used to these types of problems, you can visually be able to see the answer without these extra lines.
1230 1203 1302 1320 1032 1023 2130 2103 2301 2310 2032 2023 3210 etc
Answer:
The water temperature that produces the maximum number of salmon swimming upstream is approximately 12.305 degrees Celsius.
Step-by-step explanation:
Let
, for
.
represents the temperature of the water, measured in degrees Celsius, and
is the number of salmon swimming upstream to spawn, dimensionless.
We compute the first and second derivatives of the function:
(Eq. 1)
(Eq. 2)
Then we equalize (Eq. 1) to zero and solve for
:

And all roots are found by Quadratic Formula:
, 
Only the first root is inside the given interval of the function. Hence, the correct answer is:

Now we evaluate the second derivative at given result. That is:


According to the Second Derivative Test, a negative value means that critical value leads to a maximum. In consequence, the water temperature that produces the maximum number of salmon swimming upstream is approximately 12.305 degrees Celsius.
Correct answer is B
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