Answer:
Step-by-step explanation:
The average scores s (on a 100 point scale) for the students can be modeled by
s = 75 - 6 In(t + 1), 0 < t < 12
where t is the time in months.
a) Since the students were given an exam and then retested monthly with equivalent exams, then,
For the original exam, t = 0
Therefore,
s = 75 - 6 In(0 + 1) = 75 - 6 In1
s = 75 - 6 × 0 = 75
b) the average score after 4 months, t = 4
Therefore,
s = 75 - 6 In(4 + 1) = 75 - 6 In5
s = 75 - 9.66 = 65.34
c) s = 60
Therefore,
60 = 75 - 6 In(t + 1)
6 In(t + 1) = 75 - 60 = 15
In(t + 1) = 15/6 = 2.5
t + 1 = e^2.5 = 12.18
t = 12.18 - 1 = 11.18
t = 11 approximately
351.60 would be the answer
The result is
9
a
2
−
16
The reason is the following:
The problem is an example of a notable product: "the sum multiplied by the diference is equal to the difference of squares", that is to say:
(
a
+
b
)
⋅
(
a
−
b
)
=
a
2
−
b
2
.
By applying this to our question, we obtain that:
(
3
a
−
4
)
⋅
(
3
a
+
4
)
=
(
3
a
)
2
−
(
4
)
2
=
9
a
2
−
16
.
