y = sqrt(9 * 16).
This formula is derived because of similar parts of similar right triangles.
It is called the geometric mean which you can google for right triangles that share a common side.
y = sqrt(144)
y = 12
D is the only possible answer.
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x = sqrt(9^2 + 12^2)
x = sqrt(81 + 144)
x = sqrt(225)
x = 15
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z = sqrt( (9 + 16)^2 - 15^2)
z = sqrt( 25^2 - 15^2)
z = sqrt(625 - 225)
z = sqrt(400)
z = 20
Answer D
z =