Question

Suppose y is inversely proportional to x and the constant of proportionality equals 4. What is the minimum of the sum of x and y if x and y are both positive?

Answer 1

y = 4/x huh?

minimum...does this have something to do with calculus?

Answer 2

yes this is a calculus problem

Answer 3

y=4x^(-1)
y'=-4/x^2

Answer 4

ohh wait lol wrong approach

Answer 5

minimize x+y

Answer 6

x+y=x+4x^(-1)
minimize f(x)=x+4x^(-1)

Answer 7

f'(x)= 1 -4x^(-2)

Answer 8

so take derivative and set it to zero?

Answer 9

1-4x^(-2)=0
x^2-4=0
x=+/-2
but since x is positive, we take x=2

Answer 10

that means y=4/x=4/2=2

Answer 11

the answer's 2? i tried 2 earlier but my hw site said it was wrong.

Answer 12

minimum is 4.. 2+2 is 4

Answer 13

o

Answer 14

wait how did you go from that 1-4x^(-2)=0 to that
x^2-4=0