The picture in the attached figure
we know that
The Intersecting Secants Theorem, states that
''If two secant segments are drawn to a circle from an exterior point, then the product of the measures of one secant segment and its external secant segment is equal to the product of the measures of the other secant segment and its external secant segment''
so
in this problem
(x+DC)*DC=(AB+BC)*BC
AB=42
BC=18
CD=4
(x+4)*4=(42+18)*18
4x+16=1080
4x=1080-16
x=1064/4
x=266
the answer is
x=266
we know that
The Intersecting Secants Theorem, states that
''If two secant segments are drawn to a circle from an exterior point, then the product of the measures of one secant segment and its external secant segment is equal to the product of the measures of the other secant segment and its external secant segment''
so
in this problem
(x+DC)*DC=(AB+BC)*BC
AB=42
BC=18
CD=4
(x+4)*4=(42+18)*18
4x+16=1080
4x=1080-16
x=1064/4
x=266
the answer is
x=266