Answer:
Step-by-step explanation:
This is a related rates problem from calculus using implicit differentiation. The main equation is Pythagorean's Theorem. Basically, what we are looking for is [tex]\frac{dx}{dt}[/tex] when y = 6 and [tex]\frac{dy}{dt}=-2[/tex].
The equation for Pythagorean's Theorem is
[tex]x^2+y^2=c^2[/tex] where x and y are the legs and c is the hypotenuse. The length of the hypotenuse is 10, so when we find the derivative of this function with respect to time, and using implicit differentiation, we get:
[tex]2x\frac{dx}{dt}+2y\frac{dy}{dt}=0[/tex] and divide everything by 2 to simplify:
[tex]x\frac{dx}{dt}+y\frac{dy}{dt}=0[/tex]. Looking at that equation, it looks like we need a value for x, y, [tex]\frac{dx}{dt}[/tex] and [tex]\frac{dy}{dt}[/tex].
Since we are looking for [tex]\frac{dx}{dt}[/tex], that can be our only unknown and everything else has to have a value. So what do we know?
If we construct a right triangle with 10 as the hypotenuse and use 6 for y, we can solve for x (which is the only unknown we have, actually). Using Pythagorean's Theorem to solve for x:
[tex]x^2+6^2=10^2[/tex] and
[tex]x^2+36=100[/tex] and
[tex]x^2=64[/tex] so
x = 8.
NOW we can fill in the derivative and solve for [tex]\frac{dx}{dt}[/tex].
Remember the derivative is
[tex]x\frac{dx}{dt}+y\frac{dy}{dt}=0[/tex] so
[tex]8\frac{dx}{dt}+6(-2)=0[/tex] and
[tex]8\frac{dx}{dt}-12=0[/tex] and
[tex]8\frac{dx}{dt}=12[/tex] so
[tex]\frac{dx}{dt}=\frac{12}{8}=\frac{6}{4}=\frac{3}{2}=1.5 m/sec[/tex]
