Please help, this chapter was on derivatives...

Work Shown:

Before we can use derivatives, we need to find the value of s when (x,y) = (15,20)

s^2 = x^2+y^2

s^2 = 15^2+20^2

s^2 = 225+400

s^2 = 625

s = sqrt(625)

s = 25

Now we can apply the derivative to both sides to get the following.  Don't forget to use the chain rule.

s^2 = x^2 + y^2

d/dt[s^2] = d/dt[x^2 + y^2]

d/dt[s^2] = d/dt[x^2] + d/dt[y^2]

2s*ds/dt = 2x*dx/dt + 2y*dy/dt

2(25)*ds/dt = 2(15)*5 + 2(20)*(10)

50*ds/dt = 150 + 400

50*ds/dt = 550

ds/dt = 550/50

ds/dt = 11

Side note: The information t = 40 is never used. It's just extra info.

the answer to 1/4x+5/3x-4=2-1/12x is x=3

hope this if needed hmu