Question

Tolong bantu jawab dong.
Suatu deret aritmetika mempunyai suku ke-4=43. Jml suku ke-5 & suku ke-7 adl 106. Jml 10 suku pertama deret tsb adl.....

Answer 1

U5 = a+4b
U7 = a+6b
U4 = a+3b = 43 ...(1)
106 = 2a + 10b
(43 = a + 3b)2 =>86 = 2a + 6b
20 = 4b
b = 5
Sub ...(1)
a+3 x 5 = 43
a = 43-15 = 28
S10 = 10/2(2 x 28 + 9x5)
S10 = 5(56+45)
S10 = 505

Answer 2

U4 = 43 
U4 = a + 3b = 43
U5 + U7 =106
a + 4b + a + 6b = 106
2a + 10b = 106
a + 5b = 53

a + 5b = 53
a + 3b = 43
     2b = 10
        b = 5
a + 3(5) = 43
a = 43 - 15 = 28

Sn = n/2 (2a + (n-1)b)
S10 = 10/2 (2(28) + 9(5))
S10 = 5 (56 + 45)
S10 = 5(101)
S10 = 505