Option C:
x = 6 units
Solution:
QR = 7 units, RS = 5 units, UT = 4 units and ST = x
If two secants intersect outside a circle, the product of the secant segment and its external segment s equal to the product of the other secant segment and its external segment.
⇒ SR × SQ = ST × SU
⇒ 5 × (5 + 7) = x × (x + 4)
⇒ 5 × 12 = x² + 4x
⇒ 60 = x² + 4x
Subtract 60 from both sides.
⇒ 0 = x² + 4x - 60
Switch the sides.
⇒ x² + 4x - 60 = 0
Factor this expression, we get
(x - 6)(x + 10) = 0
x - 6 = 0, x + 10 = 0
x = 6, x = -10
Length cannot be in negative measures.
x = 6 units
Option C is the correct answer.
