In an AP, if d = – 4, n = 7


In an AP, if d = – 4, n = 7 and an = 4, then a is equal to

(a) 6                            

(b) 7                       

(c) 20                           

(d) 28


(d) In an AP $a_{n}=a+(n-1) d$

$\Rightarrow \quad 4=a+(7-1)(-4) \quad$ [by given conditions]

$\Rightarrow \quad 4=a+6(-4)$

$\Rightarrow \quad 4+24=a$

$\therefore \quad a=28$

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