Vivek Dadu

This question annoys me as a faculty. Because this is a really bad way to think and makes the parents and children vulnerable to being exploited easily by teachers and coaching institutes, the truth is that if your child is really interested in science subjects then you need to make sure that he is in company of a teacher who helps him explore the subject independently. If that happens dont worry about IIT JEE till class 10th, 2 years i.e. class 11th and 12th will be more than enough to prepare for such a child. On the other hand if your child is not interested in science subjects at all then in any case their is no use pitting him for IIT JEE preparation. In case you feel that he has the potential and just needs a right environment to develop interest then may be its a good idea to introduce him to IIT JEE foundation course in class 7th itself as sometimes a healthy competition triggers a zeal for studying in the students but be careful and watch out whether its actually having a positive effect on student.

Focus of a mirror is the point where the where the rays parallel to axis of the mirror meet after reflection. For a plane mirror, the rays parallel to the axis of the mirror fall perpendicularly to the mirror and reflected back along the same path so technically they all such reflected rays are parallel to each other and hence said to meet at infinity, hence you can say technically that focus of plane mirror lies at infinity.

As a lots of teachers above suggest, practising examples is a good way to go, but while going through examples and formulae you should not miss out on the fact that their are some fixed tricks like rationalising, using cleverly the formula for cos 2x etc. With descent practise you should be easily able to figure out which trick to use where and it will be super fun too