 Hello and welcome to the session. Let us solve the following question which says, in figure 9.15, A B C D is a parallelogram, A E is perpendicular on D C and C F is perpendicular on A D. If A B is equal to 16 cm, A E is equal to 8 cm and C F is equal to 10 cm, find A D. Let us now start with the solution and here we are given A B is equal to 16 cm, A E is equal to 8 cm and C F is equal to 10 cm and we have to find A D. Now area of a parallelogram is equal to the product of base, the corresponding altitude. So with the help of this formula we will find A D. Now the area of parallelogram A B C D is equal to, if the base is A B then the corresponding altitude is A, we have A B into A and also area of parallelogram A B C D is equal to A D into F C. Since if in this parallelogram if we consider A D as base then the corresponding altitude is C F. Now the left hand sides are equal of equation 1 and equation 2. So from 1 and 2 we have the right hand sides also equal that is A B into A E is equal to A D into F C. Now on substituting the values A B is equal to 16 into A is 8, we have to find A D and F C is 10 cm therefore A D is equal to 16 into 8 upon 10 which is equal to 128 upon 10 which is equal to 12.8. Therefore A D is equal to 12.8 cm. So this completes the session, take care and have a good day.