Question

First term and common difference of an A.P. are 6 and 3 respectively ; find S25​

Answer 1

Answer:

78

Step-by-step explanation:

S25 is

$a + (n - 1)$

a is 6

n is 25

cd is 3

substituting we get

$6 + (25 - 1) \times 3 = 6 + 24 \times 3$

$= 78$

Answer 2

Answer

here,a=6,d=3,s27=?

$Sn=n/2$  {formula}

s25=25 upon 2 [12+(25-1)x 3]

25 upon 2 x 84

=25 x 41

= 1025

therefore: s25 = 1025                                                                                                                                                                                                    

Step-by-step explanation:

how i got 84 ? = 12+24 x 3

                         =   12+ 72

                           =   84

how i got 41? = 84 divided by 2