Answer:
[tex]\sqrt{377}[/tex], or approximately 19.416
Step-by-step explanation:
This is a right triangle, so we can use the Pythagorean Theorem, which gives us that [tex]x^2 + 8^2 = 21^2[/tex]. It follows that [tex]x^2 = 377[/tex], so [tex]x = \sqrt{377} \approx 19.416[/tex].
