Answer:
The family of possible values for
are:

Step-by-step explanation:
By Linear Algebra, we can calculate the angle by definition of dot product:
(1)
Where:
- Angle between vectors, in sexagesimal degrees.
- Norms of vectors
and 
If
is acute, then the cosine function is bounded between 0 a 1 and if we know that
and
, then the possible values for
are:
Minimum (
)

Maximum (
)

With the help of a graphing tool we get the family of possible values for
are:


(a) For dx/dt=6, dy/dt = 2·6 = 12
(b) For dy/dt=2, 2 = 2·dx/dt ⇒ dx/dt = 1
_____
The value of x is irrelevant for this question.
=====
If your function is 2^x +1 or 2^(x +1), it needs to be written as such. The answer above applies to the function given.
Answer:
a) 38"
b) L = 5.7'
Step-by-step explanation:
a) Given
P = 9,500 lb/ft
Thick = 18"
We assume an allowable bearing pressure of σ = 3000 lb/sf
If Stress = Force / Area
σ = P/A
Solving for area
A = P/σ ⇒ A = 9,500 lb/ft/3000 lb/sf
⇒ A = 3.167 sf, or 3.167 ft wide, per foot of length.
⇒ A = 38" wide
We can see the pic 1 in order to understand the answer.
b) Given
P = 65,000 pounds = 65,000 lb
Thick = 18" = 1.5'
We assume an allowable bearing pressure of σ = 2000 lb/sf
If Stress = Force / Area
σ = P/A
Solving for area
A = P/σ ⇒ A = 65,000 lb/2000 lb/sf
⇒ A = 32.5 sf
then A = L² ⇒ L = √A = √(32.5 sf) = 5.7 ft
Finally L = 5.7'
We can see the pic 2 in order to understand the answer.
The technology I used in helping me solve the problem is using Microsoft Excel. I made one column for the x values which were gathered from the choices, one column for f(x) whose equation is 8^(x-9), and another column for g(x) whose equation is log(3x) + 2.
Inputing these equation to the last two columns yield the values shown in the picture.The 'NUM' means that the equation at that value of x is undefined. From the values, the correct solution would be
(0,0), (9.2,1.5) and (9.6,3.5) to the f(x) equation
(9.6,3.5) to the g(x) equation