The triangle midpoint theorem is as stated above.
In our case,
RS is joining the midpoints of NP and PQ.
Hence by the triangle midpoint theorem,
[tex]\begin{gathered} RS\parallel NQ\text{ and } \\ RS=\frac{1}{2}NQ \end{gathered}[/tex]
Therefore,
triangle PRS is similar to triangle PNQ.
This means that the ratios of their corresponding sides are equal.
[tex]\frac{NQ}{RS}=\frac{NP}{RP}[/tex]
Since R is the midpoint of NP then
[tex]\frac{NP}{RP}=2[/tex]
Therefore,
[tex]\begin{gathered} \frac{NQ}{RS}=2 \\ \Rightarrow NQ=2RS \end{gathered}[/tex]
Hence,
[tex]\begin{gathered} 9x-36=2(15-x) \\ \Rightarrow9x-36=30-2x \\ \Rightarrow9x+2x=30+36 \\ \Rightarrow11x=66 \\ \Rightarrow x=\frac{66}{11}=6 \end{gathered}[/tex][tex]\begin{gathered} \text{ Therefore,} \\ NQ=9x-36 \\ \text{gives} \\ NQ=9(6)-36=54-36=18 \end{gathered}[/tex]
Hence the measure of NQ is 18
