# Homework Help: Related Rates

1. Apr 24, 2005

### scorpa

Hi Again,

I am doing a question on related rates that I have become stuck on.

The height (h) of an equilateral triangle is increasing at a rate of 3cm/min. How fast is the area changing when h is 5cm?

I know that the area of a triangle is bh/2, but after that I am stuck I tried deriving it using the chain rule so that I could substitute h and the rate of h, but I don't think that i was doing it the right way. If anyone could direct me here I would really appreciate the help.

2. Apr 24, 2005

### Jameson

Here are some things to consider, the height "h" of an equilateral triangle is

$$\frac{1}{2}\sqrt{3}s$$

where "s" is the length of one side.

The area of this triangle is equal to

$$\frac{1}{2}sh$$

See any substitutions?

3. Apr 24, 2005

### futb0l

$$\frac{dA}{dt} = \frac{dh}{dt} * \frac{dA}{dh}$$