tolong yaa pke cara makasih

#14

Dik. Barisan deret aritmatika :
u1= 10 & u28 = 91.
Dit. Beda (b) ?

Jawab...

a = 10
u28 = a + 27b 
91 = 10 + 27b
91 - 10 = 27b
81 = 27b
b = 81/27
b = 3         ................... (B)

#15 

Dik. Barisan deret aritmatika :
-98, -95, -92, -89, ....
Dit. S50 ?

Jawab...

a = -98
b = u2 - u1 = -95 - (-98) = 3

Sn = n/2 (2a + (n - 1) b)
S50 = 50/2 (2(-98) + (49) (3))
S50 = 25 (-196 + 147)
S50 = 25 (-49)
S50 = -1225 .......................     (B)

#13 

Dik. barisan deret aritmatika :
3, 11/2, 8, 21/2 , ..... 98 atau a = 3 b = u2 - u1 = 5/2 & Un = 98.
Dit. u31 ?

Jawab...

u31 = a + 30b
u31 = 3 + 30 (5/2)
u31 = 3 + 75
u3 = 78 ......................................   (B)


Semoga membantu... ^_^