How fast is the area of rectangle increasing?
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The length of a rectangle is increasing at a rate of 8 cm/s and its width is increasing at a rate of $3$ cm/s . When the length is 20 cm and the width is 10 cm, how fast is the area of the rectangle increasing? So on internet I found a solution but I didn't do that way and I am still thinking that I am not wrong but the answer is not the same. I am gonna write both the solutions which I found on int and by myself and I will be waiting your help. Which I found on the int: $A=lw$ then take derivative $frac{dA}{dt}= frac{dl}{dt}.w + l.frac{dw}{dt}$ using given number $frac{dA}{dt}= (8)(10) + (20)(3)$ My answer: given numbers--> $frac{dl}{dt}= 8$ , $frac{dw}{dt}=3$ , $l=20$ , $w =10$ so $A=wl$ when I wanna write $w$ in terms of $l$ ----> $l=2w$ so $A=2w*w$ when I ta...