Respuesta :

Answer:

x=8.4

Step-by-step explanation:

[tex](2x)^{2} +12.6^{2} =21^{2} \\\\4x^{2} +158.76=441\\\\4x^{2}441-158.76\\\\4x^{2} =282.24\\\\x^{2} =70.56\\\\x=8.4[/tex]

hope it helps....

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