SOLUTION: During an illness, a patient’s temperature (in C) is given by the function: y = 37 + 0.9t - 0.075t2, where t is the number of days since the illness developed. (a) Calcu

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Question 1162490: During an illness, a patient’s temperature (in C) is given by the function:
y = 37 + 0.9t - 0.075t2, where t is the number of days since the illness developed.
(a) Calculate the maximum temperature during the illness, and when it occurred.
(b) When did the patient’s temperature return to normal (37 C)?

Found 3 solutions by Cromlix, MathTherapy, ikleyn:
Answer by Cromlix(4381) About Me  (Show Source):
You can put this solution on YOUR website!
Hi,
a) y = 37 + 0.9t - 0.075t^2
dy/dx = 0.9 - 0.075t
dy/dx = 0
0.9 - 0.075t = 0
- 0.075t = - 0.9
0.075t = 0.9 (Multiply both sides by -1)
t = 0.9/0.075
t = 12
Nature Table gives value t = 12 as a max.
b) By using the factorisation equation for the equation
t = -17 or t = 29
Therefore when temperature reaches 37 degrees = 29 days.
Hope this helps :-)

Answer by MathTherapy(10549) About Me  (Show Source):
You can put this solution on YOUR website!
During an illness, a patient’s temperature (in C) is given by the function:
y = 37 + 0.9t - 0.075t2, where t is the number of days since the illness developed.
(a) Calculate the maximum temperature during the illness, and when it occurred.
(b) When did the patient’s temperature return to normal (37 C)?
The other person who responded is WRONG!!
matrix%281%2C3%2C+y%2C+%22=%22%2C+37+%2B+.9t+-+.075t%5E2%29
a) Maximum temperature during illness occurs at the point where:
Maximum temperature during illness:
b) Days that it took for temperature to return to matrix%281%2C2%2C+37%5Eo%2C+C%29:
t(0) = t(.9 - .075t)
0 = .9t - .75t OR 0 = t
0 = .9 - .075t
.075t = .9
Number of days that it took for temperature to return to matrix%281%2C2%2C+37%5Eo%2C+C%29, or
t = 0 (Day 0) signifies the INITIAL day at the beginning of the developmental stage
of the illness, when patient's INITIAL temperature was ALSO matrix%281%2C2%2C+37%5Eo%2C+C%29.
FOOD FOR THOUGHT: WHY would someone use Calculus here? Does everyone know Calculus? I think NOT!!!

Answer by ikleyn(52754) About Me  (Show Source):
You can put this solution on YOUR website!
.

            I place my post here to confirm the solution by the tutor  @Math_Therapy.


It is about the maximum value of a quadratic function.


The quadratic function  f(x) = ax^2 + bx + c  of the general form with the negative leading coefficient  a < 0

has the maximum value at  x = -b%2F%282a%29.


In this case, a= -0.075, b= 0.9;  therefore, the maximum temperature is achieved at  

    
    t = -0.9%2F%282%2A%28-0.075%29%29 = %28-0.9%29%2F%28-0.15%29 = 6 days.    ANSWER


The maximum temperature  T%5Bmax%5D  is equal to the value of the given function at t= 6 :


    T%5Bmax%5D = -0.9%2A6%5E2+%2B+0.075%2A6+%2B+37 = 39.7 °C.    ANSWER

All questions are answered and the problem is solved.

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On finding the maximum/minimum of a quadratic function see the lessons
    - HOW TO complete the square to find the minimum/maximum of a quadratic function
    - Briefly on finding the minimum/maximum of a quadratic function
    - HOW TO complete the square to find the vertex of a parabola
    - Briefly on finding the vertex of a parabola
in this site.

Also,  you have this free of charge online textbook in ALGEBRA-I in this site
    - ALGEBRA-I - YOUR ONLINE TEXTBOOK.

The referred lessons are the part of this textbook under the topic "Finding minimum/maximum of quadratic functions".


Save the link to this online textbook together with its description

Free of charge online textbook in ALGEBRA-I
https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson

to your archive and use it when it is needed.