When to lines intersect they create four angles. Each angle is opposite to another and form a pair of what are called opposite angles. Angles a and c are opposite angles. Angles b and d are opposite angles. Opposite angles are equal.
The probability of the computer not containing neither a virus nor a worm is expressed as P(∩) , where P() is the probability that the event V doesn't happen and P() is the probability that the event W doesn't happen.