Partial derivative is derivative over only 1 variable.
here we have 2 variables so it depends on which variable you want to make partial derivative.
case 1.
df/dx = -3y
case 2
df/dy = 5y^4 - 3x
Consider the circle with center X, as shown in the figure.
Draw the diameter of the circle which is parallel to cherd AB, as shown in the figure.
Since the diameter and AB are parallel, then the line segment XC which bisects AB at C, will be perpendicular to AB.
SO triangle XCB is a right triangle. Thus the length of CX, by the Pythagorean theorem is

units.
Answer: 8 units
Consider triangle XYZ with vertices at points X(1,-3), Y(3,0) and Z(-1,-1). If triangle XYZ is reflected across the line y = 1, then the rule of reflection is
(x,y)→(x,-y+2).
The image X' of point X will have coordinates according to the given rule:
X(1,-3)→X'(1, -(-3)+2)=X'(1,5).
Answer: correct choice is D.
I'm not sure what your book is saying about the matter but a cell phone is not usually an essential expense. If it is saying it is though, it would be an essential flexible expense.
Answer:
Choice D).
is correct.
Step-by-step explanation:
Given function graph is sinusoidal so let's compare with formula 
We know that amplitude is the height from the center line to the peak (or to the trough). From graph we can see that height from the center line to the peak is 20
So amplitude A=20
In that formula, period is given by 
From graph we see that period is 
So both must be equal


cross multiplying them gives
B=4
Clearly there is no shift so C and D are 0
Now plug these values into formula 


Hence choice D is correct.