This response is based upon your having had some background in calculus. "dx" is not introduced before that.
Take a look at the sample function y = f(x) = x^2 + 9. Here x is the independent variable; the dependent variable y changes with x.
Now, for a big jump: we consider finding the area under a curve (graph) between x = a and x = b. We subdivide that interval [a,b] into n vertical slices of area. Each of those slices has its own area: f(x)*dx, where dx represents the width of such subarea. f(x)*dx is the actual subarea. To find the total area under the curve f(x) between x= a and x = b, we add up all of these individual subareas between x = a and x = b. Note that the subinterval width is
b-a
dx = ---------- , and that dx becomes smaller and smaller as the number of
n subintervals increases.
Once again, this all makes sense only if you've begun calculus (particularly integral calculus). Do not try to relate it to earlier math courses.
Answer: 
Step-by-step explanation:
x^2+y^2=r^2 --> subtract x^2 to other side
y^2=r^2-x^2 --> square root both sides
y=sqrt(r^2-x^2)
Answer:
a
Step-by-step explanation:
a has a greater rate of change because all the numbers make sense to the problematic function :)
mercury-73.667 million mi
venus-157.86 million mi
earth-24,860 miles (40,008 km) around
mars-133.1 million mi
jupiter-557.21 million mi
saturn-1.0058 billion mi
uranus-1.8797 billion mi
neptune-2.8704 billion mi
pluto-3.2505 billion mi
im sure this is accurate
