Pertanyaan

Diketahui suku barisan geometri suku ke-1= 3 2 dan suku-3= 27 2 . Jumlah empat suku pertama adalah ...

Diketahui suku barisan geometri suku ke-1= $\frac{2}{3}$ dan suku-3= $\frac{2}{27}$ . Jumlah empat suku pertama adalah ...

N. Mustikowati

Master Teacher

Mahasiswa/Alumni Universitas Negeri Jakarta

Jawaban terverifikasi

Pembahasan

$u subscript 1 equals a equals 2 over 3 u subscript 3 equals 2 over 27 space left right arrow a r squared equals 2 over 27 space... left parenthesis asterisk times right parenthesis M a k a colon space S u b s t i t u s i k a n space n i l a i space a space k e space p e r s a m a a n space left parenthesis asterisk times right parenthesis comma space m a k a colon 2 over 3 r squared equals 2 over 27 r squared equals 1 over 9 r equals negative 1 third space atau straight space r equals 1 third P i l i h space s a l a h space s a t u space r a s i o comma space m i s a l space r equals 1 third S e h i n g g a space j u m l a h space 4 space s u k u space p e r t a m a space y a i t u colon S subscript n equals fraction numerator a open parentheses 1 minus r to the power of n close parentheses over denominator 1 minus r end fraction S subscript 4 equals fraction numerator 2 over 3 open parentheses 1 minus open parentheses 1 third close parentheses to the power of 4 close parentheses over denominator 1 minus 1 third end fraction equals fraction numerator 2 over 3 open parentheses 1 minus 1 over 81 close parentheses over denominator 2 over 3 end fraction equals 80 over 81$