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In mathematics, a function is a relation between a set of inputs (called the domain) and a set of possible outputs (called the codomain), such that each input is related to exactly one output. The concept of a function is fundamental in various branches of mathematics and has broad applications in science and engineering.

A function is typically denoted by a rule or formula that assigns each element $x$ from the domain to a unique element $y$ in the codomain. The notation $f: X \rightarrow Y$ is often used to represent a function $f$ from the domain $X$ to the codomain $Y$.

0.000075 - 2 significant figures -

Rule: in a number that has a decimal point, the zeros before the first non-zero digit are all non significant. hence the five zeros before 7 are not significant.

890000 - 2 significant figures

Rule: In a number without an explicit decimal point (i.e., integers) the zeros that follow the last non zero digit are all non significant. hence the four zeros that follow 9 are not significant.

BONUS:

0.00007500 - this has four significant figures. Even though the five zeros before 7 are not significant, the two zeros after 5 are significant.

RULE: in a number that has a decimal point, all the zeros that follow the last non-zero digit are significant.

a number which can be divided by 2

a number which cannot be divided by 2