Question

Calculate the length of direct common tangent to two circles of radii 3cm and Bern with their centres 13cm apart.

Answer 1

To find: PQ

R₁ = 3cm, R₂ = 8cm

AB= 13cm

PQ² = AB² -(R₂ -R₁)² 

⇒ PQ² = 13² - ( 8 - 3)²

⇒  PQ² = 169 - 25

⇒ PQ² = 144

⇒ PQ = 12cm 

Length of direct common tangent is 12cm