Use linear approximation, i.e. the tangent line, to approximate 27.23\displaystyle {\sqrt[{{3}}]{{{27.2}}}} as follows:
Let f(x)=x3\displaystyle {f{{\left({x}\right)}}}={\sqrt[{{3}}]{{{x}}}}. The equation of the tangent line to f(x)\displaystyle {f{{\left({x}\right)}}} at x=27\displaystyle {x}={27} can be written in the form y=mx+b\displaystyle {y}={m}{x}+{b}

where m\displaystyle {m} is:  
and where b\displaystyle {b} is:  

Using this, we find our approximation for 27.23\displaystyle {\sqrt[{{3}}]{{{27.2}}}} is