Question

Last term of ap is 28 s =144 n=a then what is . Value of a

Answer 1

Answer:

a =?

d = ?

an = a+(n-1) d

28 = a + (9-1)d

28 = a + 8d. ----- ( equation 1 )

sn = n/2 (2a + (n-1) d)

144 = 9/2 ( 2a + (9-1)d)

144(2) = 9( 2a + 8d )

288 = 18a +72d

18( 16 = a + 4d )

16 = a + 4d -------- ( equation 2)

by doing elimination method we can find the value of a and d

a+8d = 28

a+4d = 16

- - -

_________

4d = 12

d = 12/4

d = 3

___________

by putting the value of d in eq ( 2)

a + 4 ( 3) = 16

a = 16 - 12

a = 4

___________________________

therefore a = 4 AND d=3

Answer 2

$\huge\bigstar\mathfrak\blue{\underline{\underline{SOLUTION}}}$

l=28

s= 144

n= 9

$Sn = \frac{n}{2} (a + l) \\ \\ = > S9 = \frac{9}{2} (a + 28) \\ \\ = > 144 = \frac{9}{2} (a + 28) \\ \\ = > a + 28 = 32 \\ \\ = > a = 32 - 28 \\ \\ = > a = 4$

hope it helps ☺️