[tex]\implies {\blue {\boxed {\boxed {\purple {\sf { \: (r - 7)(r - 3) }}}}}}[/tex]
[tex]\sf \bf {\boxed {\mathbb {STEP-BY-STEP\:\:EXPLANATION:}}}[/tex]
[tex] {r}^{2} - 10r + 21[/tex]
[tex] = {r}^{2} - 7r - 3r + 21[/tex]
Taking [tex]r[/tex] as common from first two terms and [tex]3[/tex] from last two terms, we have
[tex] = r(r - 7) - 3(r - 7)[/tex]
Taking the factor [tex](x-7)[/tex] as common,
[tex] = (r - 7)(r - 3)[/tex]
[tex]\bold{ \green{ \star{ \orange{Mystique35}}}}⋆[/tex]
