# how did that step occur. that -1 is also root.

Here is the explanation of your doubts:

$\mathrm{Here}\mathrm{we}\mathrm{have};\phantom{\rule{0ex}{0ex}}3{\mathrm{r}}^{3}-7{\mathrm{r}}^{2}-7\mathrm{r}+3=0\phantom{\rule{0ex}{0ex}}\mathrm{To}\mathrm{find}\mathrm{the}\mathrm{roots}\mathrm{here}\mathrm{we}\mathrm{apply}\mathrm{hit}\mathrm{and}\mathrm{trial}\mathrm{rule}.\phantom{\rule{0ex}{0ex}}\mathrm{By}\mathrm{using}\mathrm{hit}\mathrm{and}\mathrm{trial}\mathrm{rule}\mathrm{if}\mathrm{we}\mathrm{put},\mathrm{r}=-1\mathrm{we}\mathrm{have};\phantom{\rule{0ex}{0ex}}3{\left(-1\right)}^{3}-7{\left(-1\right)}^{2}-7\left(-1\right)+3\phantom{\rule{0ex}{0ex}}=-3-7+7+3=0\phantom{\rule{0ex}{0ex}}\mathrm{This}\mathrm{means}-1\mathrm{is}\mathrm{root}\mathrm{of}\mathrm{this}\mathrm{cubic}\mathrm{polynomial}.$

Hope it clears your doubt! If you have still any doubts kindly post the solution along with the complete query.

Regards

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