Answer:
C
Step-by-step explanation:
What makes a function is if each input or x-value has EXACTLY one output or y-value.
a. is wrong because the x value 1, has both an output of 1 and 4
b. is wrong because -1 is repeated 4 times with all different outputs
c. is correct because each input has exactly one output. None of the x values repeat itself
d. is wrong because -1 has 2 outputs.
so this is what makes a function and what doesn't. Hope this helps!
3/8y = 9/24 since 3*3=9 and 8*3=24
4 = 64/16 since 16*4=64
3z/x = 9z/3x since 3z*3=9z and x*3=3x
Since the surface is the top part of a sphere centred on the origin, the directions of steepest descent are any vector originating from the origin (0,0).
At (5,5), the direction would be dictated by the line joining (5,5) and the origin (0,0), i.e. along <5,5> or equivalently along <1,1>.
You can also go through vector calculus to arrive at the same result.
This will help a lot if you know how to do proportions... hope I helped