Which shows the expression below in simplified form? (7.1 × 10-7) - (4 × 10-8
+118723 $$(7.1\times 10^{-7}) - (4\times 10^{-8})$$
Using the web2 site calc
this is how it is entered
(7.1*10^-7) - (4*10^-8)
and this is the output. 
$$\left({\mathtt{7.1}}{\mathtt{\,\times\,}}{{\mathtt{10}}}^{-{\mathtt{7}}}\right){\mathtt{\,-\,}}\left({\mathtt{4}}{\mathtt{\,\times\,}}{{\mathtt{10}}}^{-{\mathtt{8}}}\right) = {\mathtt{0.000\: \!000\: \!67}}$$
.+118723 $$(7.1\times 10^{-7}) - (4\times 10^{-8})$$
Using the web2 site calc
this is how it is entered
(7.1*10^-7) - (4*10^-8)
and this is the output.
$$\left({\mathtt{7.1}}{\mathtt{\,\times\,}}{{\mathtt{10}}}^{-{\mathtt{7}}}\right){\mathtt{\,-\,}}\left({\mathtt{4}}{\mathtt{\,\times\,}}{{\mathtt{10}}}^{-{\mathtt{8}}}\right) = {\mathtt{0.000\: \!000\: \!67}}$$
