Mathematics

Problem

Which of the following expressions gives the length

PT

of a tangent drawn from an external point

P

to a circle with centre

O

and radius

r

, if

OP = d

? a)

\sqrt{d^{2}+r^{2}}

d-r

\sqrt{d^{2}-r^{2}}

\dfrac{d^{2}-r^{2}}{d}