To solve the quadratic equation given by 0=x^2-9x-20, we use the quadratic formula given by:
x=[-b+\- sqrt(b^2-4ac)]/(2a)
where,
a=1,b=-9,c=-20
thus substituting the above values into our formula we get:
x=[9+\-sqrt(9^2-4(-20*1))/(2*1)
x=[9+\-sqrt(161)]/2
x=[9+sqrt161]/2 or x=[9-sqrt161]/2
Answer:
Option A is correct.
The first step in solving the inequality is:
to distribute -4 to get 
Step-by-step explanation:
The distributive property says that:

Given the inequality:

Apply the distributive property we have;

Simplify:

Therefore, the first step in solving the inequality is:
to distribute -4 to get 
Answer:
MArginal productivity: 
We can interpret this as he will reduce his time an <em>additional </em>0.0002 seconds for every <em>additional </em>yard he trains.
Step-by-step explanation:
The marginal productivy is the instant rate of change in the result for an increase in one unit of a factor.
In this case, the productivity is the time he last in the 100-yard. The factor is the amount of yards he train per week.
The marginal productivity can be expressed as:

where dt is the variation in time and dL is the variation in training yards.
We can not derive the function because it is not defined, but we can approximate with the last two points given:

Then we can interpret this as he will reduce his time an <em>additional </em>0.0002 seconds for every <em>additional </em>yard he trains.
This is an approximation that is valid in the interval of 60,000 to 70,000 yards of training.
Answer:

Step-by-step explanation:
Start by noticing that the angle
is on the 4th quadrant (between
and
. Recall then that in this quadrant the functions tangent and cosine are positive, while the function sine is negative in value. This is important to remember given the fact that tangent of an angle is defined as the quotient of the sine function at that angle divided by the cosine of the same angle:

Now, let's use the information that the tangent of the angle in question equals "-1", and understand what that angle could be:

The particular special angle that satisfies this (the magnitude of sine and cosine the same) in the 4th quadrant, is the angle 
which renders for the cosine function the value
.
Now, since we are asked to find the value of the secant of this angle, we need to remember the expression for the secant function in terms of other trig functions: 
Therefore the value of the secant of this angle would be the reciprocal of the cosine of the angle, that is: 
Let's start by visualising this concept.
Number of grains on square:
1 2 4 8 16 ...
We can see that it starts to form a geometric sequence, with the common ratio being 2.
For the first question, we simply want the fifteenth term, so we just use the nth term geometric form:


Thus, there are 16, 384 grains on the fifteenth square.
The second question begs the same process, only this time, it's a summation. Using our sum to n terms of geometric sequence, we get:



Thus, there are 32, 767 total grains on the first 15 squares, and you should be able to work the rest from here.