9.The sum of 3el and 7th terms of an A P is 6 and their product is 8.

1.	9.The sum of 3el and 7th terms of an A P is 6 and their product is 8. Find the sum of finst 20 termu d'sA.Pas in the following distribution:
Answer» Let the first term and common differrence be a and d respectivly. so,a/q3rd term=a+2d7th term=a+6d so, a+2d+a+6d=62a+8d=62(a+4d)=6a+4d=3a=3-4d..... (1) and, (a+2d)(a+6d)=8(3-4d+2d)(3-4d+6d)=8 [from (1)](3-2d)(3+2d)=8(3)^2-(2d)^2=89-4d^2=89-8=4d^21=4d^21/4=d^21/2=d so, a=3-4da=3-2a=1 Therefore, 20th term=a+19d. =1+19*1/2. =1+19/2. =21/2

9.The sum of 3el and 7th terms of an A P is 6 and their product is 8. Find the sum of finst 20 termu d'sA.Pas in the following distribution:

Answer»

Let the first term and common differrence be a and d respectivly.

so,a/q3rd term=a+2d7th term=a+6d

so, a+2d+a+6d=62a+8d=62(a+4d)=6a+4d=3a=3-4d..... (1)

and, (a+2d)(a+6d)=8(3-4d+2d)(3-4d+6d)=8 [from (1)](3-2d)(3+2d)=8(3)^2-(2d)^2=89-4d^2=89-8=4d^21=4d^21/4=d^21/2=d

so, a=3-4da=3-2a=1

Therefore, 20th term=a+19d. =1+19*1/2. =1+19/2. =21/2