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Jawaban: U2 + U6 = 26 (a + b) + (a + 5b) = 26 2a + 6b = 26 a + 3b = 13 ➡ U4 = 13 b = U5 - U4 = 18 - 13 = 5 Substitusikan nilai b ke U4a + 3(5) = 13 a + 15 = 13 a = 13 - 15 a = -2 Hitunglah Jumlah 10 suku pertama !Jawab : → Sn = n/2(2a + (n - 1).b) → S10 = 10/2(2(-2) + 9(5)) → S10 = 5(-4 + 45) → S10 = 5(41) → S10 = [tex] \underline{ \blue{205}}[/tex]Jadi, Jumlah 10 suku pertama baris aritmatika tersebut adalah → [tex] \underline{ \blue{205}}[/tex]
" Barisan Aritmatika " ___________ U⁵ = 18 U² + U⁶ = 26 __________ S¹⁰ = ? __________ U⁵ = 18 a + ( 5 - 1 ) × b = 18 a + 4b = 18 .... ( 1 ) _________ U² + U⁶ = 26 ( a + ( 2 - 1 ) × b ) + ( a + ( 6 - 1 ) × b ) = 26 a + b + a + 5b = 26 2a + 6b = 26 ..... ( 2 ) _________ ( 1 ) - ( 2 ) a + 4b = 18 | × 2 2a + 6b = 26 ______________ 2a + 8b = 36 2a + 6b = 26 _____- 2b = 10 b = 5✅ _________ a + 4b = 18 a + 4 × 5 = 18 a + 20 = 18 a = 18 - 20 a = - 2✅ _________ a = - 2 b = 5 _________ S¹⁰ = n / 2( 2a + ( n - 1 ) × b ) S¹⁰ = 10 / 2 ( 2 ( - 2 ) + ( 10 - 1 ) × 5 ) S¹⁰ = 5 ( - 4 + 45 ) S¹⁰ = 5 × 41 [tex] \huge \boxed{ \sf {S}^{10} = 205}[/tex] |