Answer: 21
Step-by-step explanation:
x is a tangent line, 56-7 is a secant line. The length is equal to the outside segment times the entire segment. Notice that the length of the outside of the segment is equal to the entire segment for the tangent line.
[tex]x^2=7(56+7)\\\\x^2=7(63)\\\\x=\sqrt{7(63)}\\\\x=\sqrt{7(7\cdot 9)}\\\\x=7\cdot 3\\\\\large\boxed{x=21}[/tex]
