Question

@Michele_Laino

Answer 1

please, note that our slope can be viewed as a function in two variable, namely:
\[our-slpe=\frac{ dy }{ dx }=f(x,y)=2x(4-y)\]
please find the values of x and y at which f(x,y)=0

Answer 2

B right?

Answer 3

please when 2x(4-y)=0?

Answer 4

8x-2xy

Answer 5

for example if x=0, what is 2x(4-y)?

Answer 6

4-y

Answer 7

no, please it is 2*0(4-y)=0

Answer 8

and if y=4, what is 2x(4-y)?

Answer 9

4-4=0

Answer 10

2x*0=0

Answer 11

so your answers are?

Answer 12

keep in mind that horizontal tangent has a slope =0

Answer 13

the third one(:

Answer 14

and dy/dx=0 at x=0 and at y=4

Answer 15

remember vertical tangent has a slope equals to infinity

Answer 16

for example is A right?

Answer 17

yes

Answer 18

and B?

Answer 19

is B right?

Answer 20

no?

Answer 21

I think yes, because also in B slope is 0 since an horizontal tabgent has to have a slope=0

Answer 22

oops... tangent has to have...