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Dari barisan aritmetika diketahui U 3 = 18 dan U 7 = 38 . Jumlah 24 suku pertama adalah...

Dari barisan aritmetika diketahui $U_{3} = 18$ dan $U_{7} = 38$ . Jumlah 24 suku pertama adalah...

786
1248
1572
3144

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$U subscript 3 equals a plus 2 b equals 18 U subscript 7 equals a plus 6 b equals 38 N i l a i space a space d a n space b space d a p a t space d i k e t a h u i space d e n g a n space m e n g g u n a k a n space a plus 2 b equals 18 fraction numerator a plus 6 b equals 48 over denominator negative 4 b equals negative 20 end fraction space minus space space space space space space space b equals 5 S u b s t i t u s i space n i l a i space space b equals 5 space k e space U subscript 3 U subscript 3 equals a plus 2 b 18 equals a plus 2 left parenthesis 5 right parenthesis a equals 8 J u m l a h space 24 space s u k u space p e r t a m a space b a r i s a n space t e r s e b u t space a d a l a h S subscript n equals n over 2 left parenthesis 2 a plus left parenthesis n minus 1 right parenthesis b right parenthesis S subscript 24 equals 24 over 2 left parenthesis 2 left parenthesis 8 right parenthesis plus left parenthesis 24 minus 1 right parenthesis 5 right parenthesis S subscript 24 equals 12 left parenthesis 16 plus 115 right parenthesis S subscript 24 equals 12 left parenthesis 131 right parenthesis equals 1572$