Related rates differentiation problem

frosty8688

35 * 4 = 140 for x, 25 * 4 = 100 for y; [itex]\frac{-2(150-140)*35+2*100*25}{\sqrt{(150-140)^{2}+ 100^{2}}}[/itex] = [itex]\frac{-2*10*35 + 5000}{\sqrt{10^{2} + 100^{2}}}[/itex] = [itex]\frac{-700 + 5000}{\sqrt{10100}}[/itex] = [itex]\frac{4300}{10\sqrt{101}}[/itex]

eumyang

Looks like you removed the 2 in the denominator, but never factored out or canceled the 2's in the numerator. Let's just forget about canceling out the 2. You should have written:
[tex]\frac{-2(150-140) \cdot 35+2 \cdot 100 \cdot 25}{2\sqrt{(150-140)^{2}+ 100^{2}}}[/tex]
(Also, don't use "*" for multiplication in LaTeX. Use "\cdot" instead.)

frosty8688

I see, my mistake. I must have missed the 2 in the denominator.

frosty8688

It would be about 21.39 km/hr

eumyang

That's what I got. You have to be careful with the algebra when solving Calculus problems. (Not easy -- I know.)