Answer:
x=16
Explanation:
use the Pythagorean theorem.
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Another way, you can do the problem is that you can see
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that 12 divided by 4 is 3 and 20 divided by 4 is 5, which is
144+b^2=400 the two numbers from the special 3,4,5 triangle, and since
-144 -144 you have figured that much out, you can multiply 4*4 and
------------------------ get 16.
b^2=256
= 16