tolong carikan jawaban no 13

a = 10°
b = 10°

Un = a + (n-1)b
200 = 10 + (n-1)10
190 = (n-1)10
19 = n - 1
n = 20

S20 = ½ . n . ( a+U20 )
= ½ . 20 . (10 + 200)
= 10 . (210)
= 2100°
= 2100°/180° π
= 11 4/6 π
= 11 2/3 π

semoga membantu. maaf kalau salah