Three 3 Ω resistors are connected to form a triangle. What is the resistance between any two of the corners ?

 2 Ω.

Requ =2R parallel R

           =2R*R/(2R + R )

           =2/3 R =2/3*3 =2

The three resistors are connected in delta connection(as triangle). By converting delta to star we get three1Ω resistors and hence the equivalent resistance between two sides becomes2Ω.

R =2Ω

1 / R =1/{(1/(3+3)) + (1/3))

R =2

2 ohm 

2 OHM

The equivalent resistance is2 ohm