The triangles are shown to be similar, therefore

The answer is 9 units
<u>Solution-</u>
Given that,
In the parallelogram PQRS has PQ=RS=8 cm and diagonal QS= 10 cm.
Then considering ΔPQT and ΔSTF,
1- ∠FTS ≅ ∠PTQ ( ∵ These two are vertical angles)
2- ∠TFS ≅ ∠TPQ ( ∵ These two are alternate interior angles)
3- ∠TSF ≅ ∠TQP ( ∵ These two are also alternate interior angles)
<em>If the corresponding angles of two triangles are congruent, then they are said to be similar and the corresponding sides are in proportion.</em>
∴ ΔFTS ∼ ΔPTQ, so corresponding side lengths are in proportion.

As QS = TQ + TS = 10 (given)
If TS is x, then TQ will be 10-x. Then putting these values in the equation



∴ So TS = 3.85 cm and TQ is 10-3.85 = 6.15 cm
X² - 8x - 20 factors to give option
B) (x - 10)(x + 2)
x² + 8x - 20 factors to give option
A) (x - 2)(x + 10)
x² - x - 20 factors to give option C) (x - 5)(x + 4)
and x² - 9x - 20 is option D) Prime.
I hope this helps!