Jumlah suku. Ke-20 dari barisan aritmatika 5,-2-9-16, adalah

<p>Rumus mencari suku</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Un= a + (n-1). b</p><p>Diketahui: &nbsp;a= suku pertama</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; b= selisih antara suku( U2- U1)&nbsp;</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; n= Nilai yang menunjukkan banyak nya &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; suku barisan aritmatika</p><p>Ditanya: suku ke 20 adalah....&nbsp;</p><p>JAWAB:</p><p>&nbsp; &nbsp;Langkah 1: cari selisih antar suku(b)&nbsp;</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Rumus: b= U2- U1</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;b= &nbsp;(-2) - (5) =-7</p><p>&nbsp; &nbsp; Langkah 2: mencari suku ke 20</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Un= a + (n-1). b</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Un= 5 + (20-1). (-7)&nbsp;</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Un= 5 + (19) . (-7)&nbsp;</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Un= 5 + (-133)&nbsp;</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Un= - 128</p><p>Maka suku ke 20 adalah -128</p>