The word "differentiability" is spelled with three syllables: /dɪfəˈrɛnʃiəbɪlɪti/. The first syllable is pronounced with the short "i" sound (/ɪ/), followed by the "uh" sound (/ə/) and then the stress falls on the "ren" syllable (/rɛn/). The fourth syllable is pronounced with the "sh" sound (/ʃ/), followed by the "ee" sound (/i/) and then the "uh" sound (/ə/). The final syllable is pronounced with the "buhl" sound (/bɪl/), followed by the "uh" sound (/ə/) and finally the unstressed "tee" syllable (/ti/).
Differentiability is a fundamental concept in calculus and analysis that refers to the property of a function to have a well-defined derivative at a specific point. A function is said to be differentiable at a point of its domain if the derivative exists and can be determined algebraically.
More precisely, a function f(x) is differentiable at a point x=a if the limit of the difference quotient, as x approaches a, exists and is finite. The difference quotient is the ratio of the change in the function values to the corresponding change in the input, given by (f(a+h)-f(a))/h, where h is a small increment of x.
Differentiability implies that a function is continuous at the point of interest, as the derivative measures the rate of change and continuity requires the function to have no abrupt jumps or discontinuities. However, not all continuous functions are differentiable, as the existence of a derivative is conditional upon the function's behavior in the infinitesimal neighborhood of a point.
Differentiability plays a crucial role in calculus, as it allows us to approximate the behavior of a function near a given point using linear approximations, such as tangent lines. It also enables the use of powerful techniques, like the chain rule and the mean value theorem, for computing derivatives and solving various problems in mathematics and science.
The term "differentiability" derives from the noun "differentia" and the suffix "-bility".
The noun "differentia" originated in Latin as a neuter singular form of the adjective "differentis", meaning "distinguishing" or "different". In Latin, "differentia" referred to the quality or attribute that distinguishes one thing from another.
The suffix "-bility" comes from the Latin word "abilitas", which means "ability" or "capability".
When these elements are combined, "differentia" and "-bility" form "differentiability", which refers to the property or capability of being differentiable. In mathematics, differentiability is the quality of a function or curve that allows for the existence of a derivative at each point.