Which of them are particular solutions to the differential equation

dy/dx = 2xy ?

Which of them is a solution to the initial value problem

dy/dx = 2xy , y(0)=1 ?

**2. **A population of bacteria, Q(t),
increases at a rate proportional at each instant
t to the size
of the population, with the coefficient of proportionality
0.06. The
time t is measured
in hours.
**(a) **Write
a differential equation for the
function Q(t).
**(b) **Find
the general solution to this equation.
**(c) **If
the initial population is 400,
how many bacteria will be present after 10
hours ?

**3. **Match the differential
equations
**(a)** dy/dx
= y
**(b)** dy/dx
= 1 + y^{2}
**(c)** dy/dx
= x .

**(I)
(II)**

**(III)**

**4. (a)**
Find the general solution to the differential equation

dy/dt = 0.3(y - 15).

**(b) **Solve
the initial value problem

dy/dt = 0.3(y - 15), y(0) = 20.

**5. **When a murder is committed,
the body, originally at 37 ^{o}
C, cools according to
Newton' s Law of Cooling. Suppose that after two hours the temperature
is 35 ^{o} C,
and that the temperature of the surrounding
air is a constant 20 ^{o} C.
**(a) **Find
the temperature, H,
of the body as a function of t,
the time in hours since the murder was committed.
**(b) **If
the body is found at 8 a.m.
at the temperature of 30 ^{o}
C, when was the murder
committed ?

**6. **Each day at noon a hospital
patient receives 4 mg
of a drug. This drug is gradually eliminated
from the system in such a way that over each 24
hour period the amount of the drug from the original dose is reduced by
30 %. On
the other hand, the patient is receiving a new 4
mg dose each day.
**(a) **How
much of the drug is present in the patient's system immediately after
noon on the 10th
day of treatment ?
**(b) **If
the regime is continued indefinitely, at what level will the amount of
the drug in the patient's system stabilize, measured immediately after
noon every day ?

**7. **Let f(x)
= cos x.
**(a) **Find
the fourth Taylor polynomial P_{4}**
**(x) of
f(x) (at
zero).
**(b) **Use
P_{4}** **(x)
to estimate the value cos
0.9 using only
simple arithmetic. Show your calculations. Compare your estimate with the
actual value cos 0.9.

**8. **Match the surfaces **(I),
(II)**, **(III)** below with the following equations:
**(a)**
z = 5 - ( x^{2} + y^{2} )
**(b)** z =
x^{2} - y^{2}
**(c)** z = .

**(I)
(II)**

**(III)**

**9. **Match the surfaces **(I),
(II)**, **(III)** in the previous problem with contour diagrams **(A)**,
**(B)**, **(C)** below. Explain briefly how you arrived
at your answers.
**(I)
(II)
(III)**

**10. **The figure below shows level curves of the function
giving the species density of breeding birds each point of the US, Canada
and Mexico.

Looking at the map, are the following statements true or false ? Explain
your answers.
**(a) **The species density at
the tip of Baja California is above 100.
**(a) **Moving
south to north across Canada, the species density increases.
**(a) **The
greatest rate of change in species density with distance is on the
Yucatan peninsula.