Question

ce of
What is the common difference
an AP whose 4 th term is - 7 & 9th
term is 3?​

Answer 1

$Let \: a \: and \: d \: are \: first \:term \: and \\common \: difference \: of \: an \: A.P$

$\boxed { \pink { n^{th} \:term (a_{n}) = a +(n-1)d }}$

$Given \: 4^{th} \:term = -7$

$\implies a + 3d = - 7 \: ---(1)$

$Given \: 9^{th} \:term = 3$

$\implies a + 8d = 3 \: ---(2)$

/* Subtract equation (1) from equation (2), we get */

$\implies a + 8d - ( a + 3d ) = 3 - (-7)$

$\implies a + 8d - a - 3d = 3 + 7$

$\implies 5d =10$

$\implies d = \frac{10}{5}$

$\implies d = 2$

Therefore.,

$\green { Required \: Common \: difference }\green {= 2}$

♪••.

Answer 2

Answer:

a4 = a + 3.d = -7, a9 = a + 8.d = 3 , a9 - a4 = 3- (-7) = 5.d = 10, So d = 10/5 = 2ans