Question

if the 3rd term of an ap is 25 and 10th term of an ap is -3 then find the 1st term?​

Answer 1

Answer:

First term of the A.P. is 33

Step-by-step explanation:

tn = a + (n-1) d ....... Formula

t3 = a + (3-1) d

25 = a + 2d ..... Equation (1)

Similarly,

t10 = a + (10-1) d

-3 = a + 9d ..... Equation (2)

Subtracting equation (2) from (1), we get,

   25 = a + 2d

-    -3 = a + 9d

  (+)   (-)  (-)    ..... Signs change

28 = -7d

d = 28/(-7)

d = -4

Substituting d = -4 in equation (1), we get,

25 = a + 2 (-4)

25 = a + (-8)

25 = a - 8

a = 25 + 8

a = 33