The 16th term of an AP is three times the 5th term. If the 12th term is 20 more the 7th term. Find the first term and the common difference

Let's take the first term as a and the common difference be d

The formula to find the nth term of an arithmetic progression is given by :

According to question, we have :

➝ a16 = 3 ( a5 )

➝ a + ( 16 - 1 )d = 3 ( a + ( 5 - 1 )d )

➝ a + 15d = 3 ( a + 4d )

➝ a + 15d = 3a + 12d

➝ 15d - 12d = 3a - a

➝ 3d = 2a

➝ 2a = 3d

➝ a = 3d/2‎ㅤ‎ㅤ‎ㅤ⸻ ( 1 )

➝ a12 - ( a7 ) = 20

➝ a + ( n - 1 )d -( a + ( n - 1 )d ) = 20

➝ a + ( 12 - 1 )d - + a + ( 7 - 1 )d ) = 20

➝ a + 11d - ( a + 6d ) = 20

➝ a - a + 11d - 6d = 20

➝ 5d = 20

➝ d = 20/ 5

➝ d = 4

➝ a = 3d / 2

➝ a = ( 3 × 4 ) / 2

➝ a = 12 / 2

➝ a = 6

x=9

step-by-step explanation: