Answer:
a) x = 14
b) The perimeter of △QRS is 77 units.
Explanation:
a) Due to the question asking for a solution using the Triangle Proportionality Theorem, it is assumed that △RQS is similar to the smaller triangle inside it.
Let us define the point at which the line inside △RQS meets line RQ as T, and the point at which that same line meets line RS as V.
Hence, △RTV ~ △RQS.
According to the Triangle Proportionality Theorem:
![(RT)/(RQ) = (TV)/(QS) = (VR)/(SR)](https://img.qammunity.org/2021/formulas/mathematics/college/m20uxdf3kulcdj197wubu839wjhngmpgba.png)
Hence, we can substitute all values that we know from the diagram:
![(2x - 2)/(2x - 2 + 13) = (TV)/(17) = (21 - 7)/(21)](https://img.qammunity.org/2021/formulas/mathematics/college/4efr953t853vg0c14tqud94rxr2nc0dnw7.png)
After getting this information, all we have to do is simplify and solve the equation:
![(2x - 2)/(2x - 2 + 13) = (21 - 7)/(21)](https://img.qammunity.org/2021/formulas/mathematics/college/xy4st76jwe6f6a02ato1p68hn55840z938.png)
![(2x - 2)/(2x + 11) = (14)/(21)](https://img.qammunity.org/2021/formulas/mathematics/college/b7vwpxr05t9tcxgjpywbyo590b2piviphe.png)
![(2x - 2)/(2x + 11) = (2)/(3)](https://img.qammunity.org/2021/formulas/mathematics/college/ysb0z7axh2zk6kjcmruzupx4xu6iytmhpi.png)
![3(2x - 2) = 2(2x + 11)](https://img.qammunity.org/2021/formulas/mathematics/college/j9gfhq4rhabioihsunpv4fwu0u5x8eei30.png)
![6x - 6 = 4x + 22](https://img.qammunity.org/2021/formulas/mathematics/college/kwemj5rlx4yl1ixp5npr0avppk2444rga2.png)
![6x - 4x = 22 + 6](https://img.qammunity.org/2021/formulas/mathematics/college/mhhie8y3msew0wzihwlzl8g0ahnemmzton.png)
![2x = 28](https://img.qammunity.org/2021/formulas/mathematics/college/t5uy9q20hre9nobqltfoj95u9q9iyvcceu.png)
![x = 14](https://img.qammunity.org/2021/formulas/mathematics/middle-school/d0o39rzhefit9rtelhq51fltqih97xv400.png)
To verify this answer, we can plug in the value of x into the equation:
![(2(14) - 2)/(2(14) - 2 + 13) = (2)/(3)](https://img.qammunity.org/2021/formulas/mathematics/college/mcm4a1mod7fif4i9dkl1m41l361u4s7ch9.png)
![(26)/(39) = (2)/(3)](https://img.qammunity.org/2021/formulas/mathematics/college/chk7ienttgyyy2irf5hz6tdf1fohigvmn6.png)
![(2)/(3) = (2)/(3)](https://img.qammunity.org/2021/formulas/mathematics/college/89lcqnr9e9auq1mpzkglj7npmq2hwo5y74.png)
Hence, after verification, we can get the answer: x = 14.
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b) To find the perimeter of △QRS, all we have to do is to add all the lengths of the sides of △QRS together.
Hence, 2(14) - 2 + 13 + 17 + 21
= 28 - 2 + 13 + 17 + 21
= 77 units
Therefore, the perimeter of △QRS is 77 units.
Hope this helped!