y'=1/[x+√(x²-a²)]*[x+√(x²-a²)]'=1/[x+√(x²-a²)]*[1+1/2√(x²-a²)*(x²-a²)]'=1/[x+√(x²-a²)]*1+2x/2√(x²-a²)]=1/[x+√(x²-a²)]*[x+√(x²-a²)]/√(x²-a²)=1/√(x²-a²)
