inii yhhh

<p>Jawaban : A. 19</p><p>&nbsp;</p><p>Ingat kembali bentuk umum persamaan parabola berikut:</p><p>y = ax² + bx + c</p><p>&nbsp;</p><p>Diketahui : parabola melalui titik-titik (1, -5), (2, 6), dan (3, 21)</p><p>&nbsp;</p><p>Maka:</p><p>titik (1, -5)</p><p>y = ax² + bx + c</p><p>-5 = a(1)² + b(1) + c</p><p>-5 = a + b + c</p><p>a + b + c = -5 ...... (i)</p><p>&nbsp;</p><p>titik (2, 6)</p><p>y = ax² + bx + c</p><p>6 = a(2)² + b(2) + c</p><p>6 = 4a + 2b + c</p><p>4a + 2b + c = 6 ...... (ii)</p><p>&nbsp;</p><p>titik (3, 21)</p><p>y = ax² + bx + c</p><p>21 = a(3)² + b(3) + c</p><p>21 = 9a + 3b + c</p><p>9a + 3b + c = 21 ...... (iii)</p><p>&nbsp;</p><p>Eliminasi (i) dan (ii)</p><p>a + b + c = -5</p><p>4a + 2b + c = 6</p><p>--------------------- -</p><p>-3a - b = -11</p><p>3a + b = 11 ................. (iv)</p><p>&nbsp;</p><p>Eliminasi (i) dan (iii)</p><p>a + b + c = -5</p><p>9a + 3b + c = 21</p><p>----------------------- -</p><p>-8a - 2b = -26</p><p>4a + b = 13 .................. (v)</p><p>&nbsp;</p><p>Eliminasi (iv) dan (v)</p><p>3a + b = 11</p><p>4a + b = 13</p><p>------------------- -</p><p>-a = -2</p><p>a = 2</p><p>&nbsp;</p><p>Substitusi nilai a ke (iv)</p><p>3a + b = 11</p><p>3(2) + b = 11</p><p>6 + b = 11</p><p>b = 11 - 6</p><p>b = 5</p><p>&nbsp;</p><p>Subtitusi nilai a dan b ke (i)</p><p>a + b + c = -5</p><p>12 + 5 + c = -5</p><p>17 + c = -5</p><p>c = -5 - 17</p><p>c = -22</p><p>&nbsp;</p><p>Sehingga:&nbsp;</p><p>a + b - c = 2 + (-5) - (-22) = 2 - 5 + 22 = 19</p><p>&nbsp;</p><p>Jadi, jawaban yang benar adalah A.</p>