Woah, 4U already? Why are you even learning implicit differentiation o_o
Anyway, if we draw our diagram we immediately notice a right angle triangle.
Hence by Pythagoras: x^2+y^2=8^2 \ \ \ x^2+y^2=64
Let us differentiate implicitly:
x^2+y^2=64 \ \ \ 2x+2y y'=0
-yy'=x \ \ \ \therefore...