Given the function
f(x)={7x−7x<07x−14x≥0\displaystyle {f{{\left({x}\right)}}}={\left\lbrace\begin{array}{cc} {7}{x}-{7}&{x}<{0}\\{7}{x}-{14}&{x}\geq{0}\end{array}\right.}

Calculate the following values:
f(−1)=\displaystyle {f{{\left(-{1}\right)}}}=  
f(0)=\displaystyle {f{{\left({0}\right)}}}=  
f(2)=\displaystyle {f{{\left({2}\right)}}}=  

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