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[Lukybear]

Two Straight roads meet an an angle of 60 degrees. A starts from the intersection and travel along one road at 40km/h. One hour later B starts from the intersection and travels along the other road at 50km/h. At what rate is the distance between them changing three hours after A starts.

 

[Shikobe]

This question is basically the same type as the question 17(Fitz book).
So, instead of using Pythagoras theorem too find the distance, you use the cosine rule and thats basically it.

 

[Lukybear]

I did. But i didnt get it. Its actuall q18 (fitz book)

Youll get something like x^2 +y^2 - xy = distance

But how do you differentiate that?

 

[lychnobity]

I did. But i didnt get it. Its actuall q18 (fitz book)

Youll get something like x^2 +y^2 - xy = distance

But how do you differentiate that?

Implicitly.

Treat y as a function, then differentiate wrt x

differentiate this: x^2 +y^2 + (- xy) = distance

and it becomes this: 2x + 2y(y') + (-y - y'x) = 0

2x + 2y'y - y - y'x = 0

2x - y + y'(2y - x) = 0

y' = (y - 2x)/(2y - x)

 

[Lukybear]

Implicitly.

Treat y as a function, then differentiate wrt x

differentiate this: x^2 +y^2 + (- xy) = distance

and it becomes this: 2x + 2y(y') + (-y - y'x) = 0

2x + 2y'y - y - y'x = 0

2x - y + y'(2y - x) = 0

y' = (y - 2x)/(2y - x)

But implicit isnt part of the 3unit course. Although i did try and the answer wasnt correct