Differentiation from the First Principle

$ \displaystyle \frac{{dy}}{{dx}}=\underset{{\delta x\to 0}}{\mathop{{\lim }}}\,\frac{{\delta y}}{{\delta x}}$ or $ \displaystyle {f}'(x)=\underset{{\delta x\to 0}}{\mathop{{\lim }}}\,\frac{{f(x+\delta x)-f(x)}}{{\delta x}}$  ဘယ္လို ျဖစ္သြားလဲ...