7,18,29,40,..... tentukan U26 dan S25! Tolong jwb y makasih

A.
a= suku pertama
b = beda
n = suku ke

a = 7
b = 11
n = 26

Un = a + (n-1)×b
= 7 + 25 ×11
=275 + 7
=282
B.
a = 7
b = 11
n = 25

Sn = n/2 (2a (n-1)b)
= 25/2 (2 × 7 ( 25 - 1) × 11)
= 25/ 2 ( 14 + 24 × 11)
= 25/2 (14+ 264)
= 25/ 2 × 278
= 25 × 139
= 3475
Semoga membantu