Question

find phone numbers in AP whose sum is 16 and sum of squares is 84

Answer 1

6 answers · Mathematics 

 Best Answer

Consider the four terms; a - 3d , a - d , a + d and a + 3d 

so ,a - 3d + a - d + a + d + a + 3d = 16 

=> 4a = 16 => a = 4 

And (a - 3d)² + (a - d)² + (a + d)² + (a + 3d)² = 84

=> 4a² + 20d² = 84 

=> 20d² = 84 - 64 

=> 20d² = 20 

=> 20d² = 20 

=> d = ± 1 

therefore: terms of A.P. = 1 , 3 , 5 , 7 or 7 , 5 , 3 , 1 -----------> (Ans)