bantuu dong

<p>U₂ = 15</p><p>U₄ = 23</p><p>&nbsp;</p><p>a.<strong> Mencari suku pertama dan beda</strong></p><p>&nbsp; &nbsp; &nbsp;b = (U₄ - U₂)/(4 - 2)</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= (23 - 15)/2</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= 8/2</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= 4</p><p>&nbsp; &nbsp; &nbsp;Beda atau selisih barisan tersebut adalah<strong> 4</strong></p><p>&nbsp; &nbsp; &nbsp;&nbsp;</p><p>&nbsp; &nbsp; &nbsp; U₂ = 15</p><p>&nbsp; &nbsp; &nbsp; U_n&nbsp; = a + (n - 1)b</p><p>&nbsp; &nbsp; &nbsp; 15 = a + (2 - 1) 4</p><p>&nbsp; &nbsp; &nbsp; 15 = a + (1)4</p><p>&nbsp; &nbsp; &nbsp; 15 = a &nbsp;+ 4</p><p>&nbsp; &nbsp; &nbsp; a = 15 - 4 = 11</p><p>&nbsp; &nbsp; &nbsp; Suku pertama (U₁) adalah <strong>11</strong></p><p>&nbsp;</p><p>b. <strong>Mencari jumlah dari suku kelima hingga suku kedua puluh</strong></p><p><strong>&nbsp; &nbsp; &nbsp;</strong>S_n = n/2 (2a + (n - 1)b)</p><p>&nbsp; &nbsp; &nbsp;S_{5 &nbsp;}= 5/2 (2(11) + (5 - 1)4)</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= 5/2 (22 + 16)</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= 5/2 (38)</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= 95</p><p>&nbsp;</p><p>&nbsp;S_{20 &nbsp;}= 20/2 (2(11) + (20 - 1)4)</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= 10 (22 + 76)</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= 10 (98)</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= 980</p><p>Jumlah suku dari suku kelima hingga suku kedua puluh = S₂₀ - S₅</p><p>_{&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;}= 980 - 95</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; = 885</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;</p><p>Jadi, Jumlah suku dari suku kelima hingga suku kedua puluh adalah <strong>885</strong> &nbsp;</p><p>&nbsp;</p>