0\\20-x=0\\x=20" alt="y=(19-x)e^{19-x}\\\\y`=(19-x)`e^{19-x}+(19-x)(e^{19-x})`=-e^{19-x}+(19-x)e^{19-x}(19-x)`=\\\\-e^{19-x}-(19-x)e^{19-x}=-e^{19-x}(1+19-x)=-e^{19-x}(20-x)\\\\y`(x)=0\\-e^{19-x}(20-x)=0\\e^{19-x}>0\\20-x=0\\x=20" align="absmiddle" class="latex-formula">
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_____________________20_____________________
min
x(min)=20