The side RS is 7 cm. For a similar triangle, the ratio of the opposite side of the two similar triangle are the same.
What is SAS similarity theorem?
ΔABC ~ ΔDEF only if the ratio of two sides of ΔABC and corresponding two sides of ΔDEF is equal, and the angle included in both sides are congruent.
Suppose the two sides of ΔABC are AB and BC, and that of DEF be DE and EF, then for SAS similarity, we need
For the similar triangle;
[tex]\rm \frac{HG}{TS} = \frac{FG}{RS} \\\\ \frac{12}{4} =\frac{21}{RS} \\\\ RS= 7 cm[/tex]
Hence, the side RS is 7 cm.]
To learn more about the SAS similarity theorem, refer to link;
https://brainly.com/question/22472034
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