3. Exponential Growth & Decay
Growth and decay is proportional to population.
dP
kP
dt
4. Exponential Growth & Decay
Growth and decay is proportional to population.
dP
kP
dt
dt 1
dP kP
5. Exponential Growth & Decay
Growth and decay is proportional to population.
dP
kP
dt
dt 1
dP kP
1 dP
t
k P
6. Exponential Growth & Decay
Growth and decay is proportional to population.
dP
kP
dt
dt 1
dP kP
1 dP
t
k P
1
log P c
k
7. Exponential Growth & Decay
Growth and decay is proportional to population.
dP
kP
dt
dt 1
dP kP
1 dP
t
k P
1
log P c
k
kt log P c
8. Exponential Growth & Decay
Growth and decay is proportional to population.
dP
kP
dt
dt 1
dP kP
1 dP
t
k P
1
log P c
k
kt log P c
log P kt c
9. Exponential Growth & Decay
Growth and decay is proportional to population.
dP
kP
dt
dt 1
dP kP
1 dP
t
k P
1
log P c
k
kt log P c
log P kt c
P e kt c
10. Exponential Growth & Decay
Growth and decay is proportional to population.
dP
kP
dt
dt 1
dP kP
1 dP
t
k P
1
log P c
k
kt log P c
log P kt c
P e kt c
P e kt e c
11. Exponential Growth & Decay
Growth and decay is proportional to population.
dP
kP
dt
dt 1
dP kP
1 dP
t
k P
1
log P c
k P Ae kt
kt log P c
log P kt c
P e kt c
P e kt e c
12. Exponential Growth & Decay
Growth and decay is proportional to population.
dP
kP
dt
dt 1
dP kP
1 dP
t
k P
1
log P c
k P Ae kt
kt log P c
P = population at time t
log P kt c
P e kt c A = initial population
P e kt e c k = growth(or decay) constant
t = time
13. e.g.(i) The growth rate per hour of a population of bacteria is 10% of
the population. The initial population is 1000000
14. e.g.(i) The growth rate per hour of a population of bacteria is 10% of
the population. The initial population is 1000000
a) Show that P Ae 0.1t is a solution t o the differential equation.
15. e.g.(i) The growth rate per hour of a population of bacteria is 10% of
the population. The initial population is 1000000
a) Show that P Ae 0.1t is a solution t o the differential equation.
P Ae 0.1t
16. e.g.(i) The growth rate per hour of a population of bacteria is 10% of
the population. The initial population is 1000000
a) Show that P Ae 0.1t is a solution t o the differential equation.
P Ae 0.1t
dP
0.1Ae 0.1t
dt
17. e.g.(i) The growth rate per hour of a population of bacteria is 10% of
the population. The initial population is 1000000
a) Show that P Ae 0.1t is a solution t o the differential equation.
P Ae 0.1t
dP
0.1Ae 0.1t
dt
0.1P
18. e.g.(i) The growth rate per hour of a population of bacteria is 10% of
the population. The initial population is 1000000
a) Show that P Ae 0.1t is a solution t o the differential equation.
P Ae 0.1t
dP
0.1Ae 0.1t
dt
0.1P
1
b) Determine the population after 3 hours correct to 4 significant figures.
2
19. e.g.(i) The growth rate per hour of a population of bacteria is 10% of
the population. The initial population is 1000000
a) Show that P Ae 0.1t is a solution t o the differential equation.
P Ae 0.1t
dP
0.1Ae 0.1t
dt
0.1P
1
b) Determine the population after 3 hours correct to 4 significant figures.
2
when t 0, P 1000000
A 1000000
P 1000000 e 0.1t
20. e.g.(i) The growth rate per hour of a population of bacteria is 10% of
the population. The initial population is 1000000
a) Show that P Ae 0.1t is a solution t o the differential equation.
P Ae 0.1t
dP
0.1Ae 0.1t
dt
0.1P
1
b) Determine the population after 3 hours correct to 4 significant figures.
2
when t 0, P 1000000 when t 3 .5, P 1000000 e 0.13.5
A 1000000 1 4 19 000
P 1000000 e 0.1t
21. e.g.(i) The growth rate per hour of a population of bacteria is 10% of
the population. The initial population is 1000000
a) Show that P Ae 0.1t is a solution t o the differential equation.
P Ae 0.1t
dP
0.1Ae 0.1t
dt
0.1P
1
b) Determine the population after 3 hours correct to 4 significant figures.
2
when t 0, P 1000000 when t 3 .5, P 1000000 e 0.13.5
A 1 000000 1 4 19 000
P 1000000 e 0.1t
1
after 3 hours there is 1419000 bacteria
2
22. (ii) On an island, the population in 1960 was 1732 and in 1970 it was
1260.
a) Find the annual growth rate to the nearest %, assuming it is
proportional to population.
23. (ii) On an island, the population in 1960 was 1732 and in 1970 it was
1260.
a) Find the annual growth rate to the nearest %, assuming it is
proportional to population.
dP
kP
dt
24. (ii) On an island, the population in 1960 was 1732 and in 1970 it was
1260.
a) Find the annual growth rate to the nearest %, assuming it is
proportional to population.
dP
kP
dt
P Ae kt
25. (ii) On an island, the population in 1960 was 1732 and in 1970 it was
1260.
a) Find the annual growth rate to the nearest %, assuming it is
proportional to population.
dP
kP
dt
P Ae kt
when t 0, P 1732
A 1732
P 1732e kt
26. (ii) On an island, the population in 1960 was 1732 and in 1970 it was
1260.
a) Find the annual growth rate to the nearest %, assuming it is
proportional to population.
dP when t 10, P 1260
kP
dt
i.e. 1260 1732e10 k
P Ae kt
when t 0, P 1732
A 1732
P 1732e kt
27. (ii) On an island, the population in 1960 was 1732 and in 1970 it was
1260.
a) Find the annual growth rate to the nearest %, assuming it is
proportional to population.
dP when t 10, P 1260
kP
dt
i.e. 1260 1732e10 k
P Ae kt 1260
e10 k
when t 0, P 1732 1732
A 1732
P 1732e kt
28. (ii) On an island, the population in 1960 was 1732 and in 1970 it was
1260.
a) Find the annual growth rate to the nearest %, assuming it is
proportional to population.
dP when t 10, P 1260
kP
dt
i.e. 1260 1732e10 k
P Ae kt 1260
e10 k
when t 0, P 1732 1732
A 1732 1260
10k log
P 1732e kt 1732
1
k log 1260
10 1732
29. (ii) On an island, the population in 1960 was 1732 and in 1970 it was
1260.
a) Find the annual growth rate to the nearest %, assuming it is
proportional to population.
dP when t 10, P 1260
kP
dt
i.e. 1260 1732e10 k
P Ae kt 1260
e10 k
when t 0, P 1732 1732
A 1732 1260
10k log
P 1732e kt 1732
1
k log 1260
10 1732
k 0.0318165
30. (ii) On an island, the population in 1960 was 1732 and in 1970 it was
1260.
a) Find the annual growth rate to the nearest %, assuming it is
proportional to population.
dP when t 10, P 1260
kP
dt
i.e. 1260 1732e10 k
P Ae kt 1260
e10 k
when t 0, P 1732 1732
A 1732 1260
10k log
P 1732e kt 1732
1
k log 1260
10 1732
k 0.0318165
growth rate is - 3%
31. b) In how many years will the population be half that in 1960?
32. b) In how many years will the population be half that in 1960?
when P 866, 866 1732e kt
33. b) In how many years will the population be half that in 1960?
when P 866, 866 1732e kt
1
e
kt
2
1
kt log
2
1 1
t log
k 2
34. b) In how many years will the population be half that in 1960?
when P 866, 866 1732e kt
1
e
kt
2
1
kt log
2
1 1
t log
k 2
t 21.786
35. b) In how many years will the population be half that in 1960?
when P 866, 866 1732e kt
1
e
kt
2
1
kt log
2
1 1
t log
k 2
t 21.786
In 22 years the population has halved
36. b) In how many years will the population be half that in 1960?
when P 866, 866 1732e kt
1
e
kt
2
1
kt log
2
1 1
t log
k 2
t 21.786
In 22 years the population has halved
Exercise 7G; 2, 3, 7, 9, 11, 12