tolong kak :)

<p>a. 3 + 9 + 27 + .....</p><p>&nbsp; &nbsp; &nbsp;a = 3</p><p>&nbsp; &nbsp; &nbsp;r = 9/3 = 3</p><p>&nbsp; &nbsp; &nbsp;U_n = ar^{n - 1}</p><p>^{&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;} = 3. 3^{n - 1}</p><p>^{&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;}= 3ⁿ</p><p>&nbsp; &nbsp; &nbsp;Rumus suku ke-n adalah <strong>U_n = 3ⁿ&nbsp;</strong></p><p>&nbsp; &nbsp; &nbsp;U₈ = 3⁸</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= 6.561</p><p>&nbsp;</p><p>b. &nbsp;1 + 4 + 16 + 64 + .....</p><p>&nbsp; &nbsp; &nbsp; a = 1</p><p>&nbsp; &nbsp; &nbsp; r = 4/1 = 4</p><p>&nbsp; &nbsp; &nbsp; U_n = ar^{n - 1}</p><p>^{&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;} = 1. 4^{n - 1}</p><p>^{&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;}= 4^n-1</p><p>&nbsp; &nbsp; &nbsp;Rumus suku ke-n adalah <strong>U_n = 4^n-1&nbsp;</strong></p><p>&nbsp; &nbsp; &nbsp;U₈ = 4^8-1</p><p>^{&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;}= 4⁷</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= 16.384</p><p>&nbsp;</p><p>c. 20 - 10 + 5 - .....</p><p>&nbsp; &nbsp; &nbsp;a = 20</p><p>&nbsp; &nbsp; &nbsp;r = -10/20 = -1/2</p><p>&nbsp; &nbsp; &nbsp;U_n = ar^{n - 1}</p><p>^{&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;} = 20. (-1/2)^{n - 1}</p><p>^{&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;}= -40. (-1/2)ⁿ</p><p>&nbsp; &nbsp; &nbsp;Rumus suku ke-n adalah <strong>U_n = -40. (-1/2)ⁿ</strong></p><p>&nbsp; &nbsp; &nbsp;U₈ = -40. (-1/2)ⁿ</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= -40. (-1/2)⁸&nbsp;</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= -40 . (1/256)</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= -5/32</p><p>&nbsp;</p><p>d. 4 - 8 + 16 - 32 + ....</p><p>&nbsp; &nbsp; &nbsp;a = 4</p><p>&nbsp; &nbsp; &nbsp;r = -8/4 = -2</p><p>&nbsp; &nbsp; &nbsp;U_n = ar^{n - 1}</p><p>^{&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;} = 4. (-2)^{n - 1}</p><p>^{&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;}= 4 . (-2)^n-1</p><p>^{&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;}= (-2)ⁿ⁺¹</p><p>&nbsp; &nbsp; &nbsp;Rumus suku ke-n adalah <strong>U_n = (-2)ⁿ⁺¹</strong></p><p>&nbsp; &nbsp; &nbsp;U₈ = (-2)ⁿ⁺¹</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= (-2)⁸⁺¹</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= (-2)⁹</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= -512</p>