Why we have to take which 3 cases only which u taught and why can we not to take bc=ef and how can we know that we have to take 3cases which u taught

IF the 3rd ana 9th terms of an AP. ara 4 and -8 respectively, which term of this AP. is zero 

What will be the accounting entry for a sale made through e-commerce operator and the entry of the commission invoice received at the month end ?The commission invoice which they issue doesn't include the amount of TCS collected by them transaction wise during that particular month.When should i deduct the amount of expenses charged by e-commerce operators to send my product to direct customer ? Should i record them at the point of day on sale or at the point of receipt received of that particular product sold ?

Exercise 7.4 q6 class 10

Solve the following pair of equations by reducing them to a pair of linear equations 4/x+3y=14,3/x-4y=23

4/x+3y=14,3/x-4y=23

Obtain all other zeroes of 3x4+6x3-2x2-10x-5 if two of its zeroes are square root of 5/3 and -square root of 5/3

There are ten prizes , five A's, three B's, two C's, placed in a identical sealed envelopes for the top ten contestants in a mathematics contest. the prizes are awarded by allowing winners to select an envelope at random from those remaining .when the 8th contestant goes to select the prize , the probability that the remaining three prizes are one A, one B, one C , is

The angle of elevation of a cloud from a point 60m above a lake is 30 and the angle of depression to its reflection in the lake is 60 find the length find the height of the cloud