Answer:
x = ~8.9
Explanation:
a^2 + b^2 = c^2
c is the long side
a and b are the other two shorter sides
this means
x^2 + 19^2 = 21^2
x^2 + 361 = 441
x^2 = 441- 361
x^2 = 80
square root of 80 = ~8.9
8.9
=8.9444
rounded = 8.9
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