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Hindi
8. Sequences and Series
easy

સમાંતર શ્રેણીનું $7$ મુ પદ $40$ હોય, તો તેના પ્રથમ $13$ પદોનો સરવાળો........ થશે.

A

$53$

B

$520$

C

$1040$

D

$2080$

Solution

$t_n = a(n – 1)d$ અને $t_7 = 40$  

$a + 6d = 40$

$2a + 12d = 80$

હવે $\text{,}\,\,{{S}_{n}}=\frac{n}{2}[2a+(n-1)d]\,\,\,\,$

$\therefore \,\,{{S}_{13}}=\frac{13}{2}[2a+12d]=\frac{13}{2}(80)=520$

Standard 11
Mathematics

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