Pls pls i’m really confused could someone explain to me pls

a circle with radius z is shown below the diagram is not to scale. what is the value of x. round to the nearest tenth

11.6

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Explanation:

See the attached image for a visual reference

The distance from point D to E is 21 units. Point C is the midpoint, so CD is 10.5 units long (21/2 = 10.5)

We have a right triangle ACD. The legs are
AC = 5
CD = 10.5
The hypotenuse is 
AD = x
Because AD is another radius of the same circle

Use the pythagorean theorem to find x
a^2 + b^2 = c^2
5^2 + 10.5^2 = x^2
25 + 110.25 = x^2
135.25 = x^2
x^2 = 135.25
x = sqrt(135.25)
x = 11.629703349613
which rounds to 11.6 when rounding to the nearest tenth (one decimal place)