Tolong jngn ngasal dan jwb dngn lengkap dngn jalan ny​

semoga bermanfaat…………..

Penjelasan dengan langkah-langkah:

a. 1 + 3 + 5 + 7 +……. a = 1 b = 2

S(20) = 1/2n (2a + (n – 1) b)

= 1/2 (20) (2 + (20 – 1) (2))

= 10 (2 + 19 (2))

= 10 (2 + 38)

= 10 (40)

= 400

b. S(19) = 1/2n (2a + (n – 1) b)

= 1/2 (19) (2 + (19-1) (2))

= 19/2 (2 + 18 (2))

= 19/2 (2 + 36)

= 19/2 (38)

= 361