tentukan unsur yang diminta dari deret aritmatika berikut 1. a=2, s22=737, b= 2. b=5, u10=46, s15= 3. u4=9, u7=18, s10=

Sn = 1/2n [ 2a + ( n – 1 ) b ] <<== acuan

Un = a + (n-1) b <<==== acuan



1. a = 2 , S22 = 737 , b =....???

Sn = 1/2n [ 2a + ( n – 1 ) b ]

s22 = 22/2 [ 2 (2) + (21) b ]

737 = 11 [ 4 + 21 b ]

737 / 11 = 4 + 21 b

21 b = 67 - 4

b = 63/21

b = 3 ===>>> lets Rock



2. b = 5 , u10 = 46 , s15..???

Un = a + (n-1) b

U10 = a + (9) 5

46 = a + 45

a = 1 <<====

Sn = 1/2n [ 2a + ( n – 1 ) b ]

s15 = 15/2 ( 2(1) + 14 (5) )

s15 = 15/2 ( 72 )

s15 = 540 <<==== Rock It



3. u4 = 9 , u7 = 8 , s10...????

U4 = 9
a + 3b = 9

a = 9 - 3b ==>>> acuan

U7 = 8
a + 6b = 8

9 - 3b + 6b = 8

3b = 8 - 9

b = -1/3 ==>_ subs ke nilai U4 utk nilai a

a + 3b = 9

a + 3 (-1/3) = 9

a - 1 = 9

a = 10 <<====

Sn = 1/2n [ 2a + ( n – 1 ) b ]

S10 = 10/2 [2 (10) + 9 (-1/3) ]

S10 = 5 [ 20 - 3 ]

s10 = 5 ( 17 )

s10 = 85 ===>__ Rock Finish