Question

(x) given l=28, S= 144, and there are total 9 terms. Find a.​

Answer 1

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Given :

l (last term) = 28

s ( sum of all terms) = 144

n (number of terms) = 9

to find :

a ( first term) = ?

Solution :

As we know,

$\boxed{ \bf{s = \frac{n}{2} \times (a + l)}}$

putting values

$\mathrm{144 = \frac{9}{2} \times (a + 28) } \\ \\ \mathrm{a + 28 = 144 \times \frac{2}{9} } \\ \\ \mathrm{a + 28 = 32} \\ \\ \mathrm{ a = 32 - 28} \\ \\ \boxed{ \bf{a = 4}}$

Therefore,

value of first term is 4 .

Answer 2

Answer:

S=144 l=28 n=9

Sn=n/2(a+l)

9/2(a+28)=144

a+28=32

a=4