tolong jawab pakai cara ya kak. terimakasih

<p>Jawaban yang benar adalah D. f(x) = -x² - 2x - 8</p><p>&nbsp;</p><p>Pembahasan :</p><p>f(x) = ax² + bx + c</p><p>&nbsp;</p><p>Substitusikan (0, -8)</p><p>&nbsp;f(x) = ax² + bx + c</p><p>-8 = c</p><p>c = -8</p><p>&nbsp;</p><p>Titik Puncak (-1,-7)</p><p>x = -1</p><p>x = -b/2a</p><p>-1 = -b/2a</p><p>-2a = -b</p><p>b = 2a &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; (1) &nbsp;</p><p>&nbsp;</p><p>y = -7</p><p>y = (b² - 4ac)/-4a</p><p>-7 = (b² - 4ac)/-4a</p><p>28a = b² - 4ac</p><p>28a = b² - 4a(-8) &nbsp; &nbsp; &nbsp; &nbsp;( c diganti dengan -8)</p><p>28a = b² + 32a</p><p>28a - 32a = b²</p><p>-4a = b² &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;(2)</p><p>Substitusikan persamaan (1) ke persamaan (2)</p><p>b² = -4a</p><p>(2a)² = -4a</p><p>4a² = -4a</p><p>4a² + 4a = 0</p><p>4a(a + 1) = 0</p><p>a = 0 atau a = -1</p><p>Kita pakai a = -1</p><p>b = 2(-1) = -2</p><p>&nbsp;</p><p>Substitusikan a = -1, b = -2 dan c = -8 ke rumus umum fungsi</p><p>f(x) = ax² + bx + c</p><p>f(x) = -x² - 2x - 8</p>