Parabola y = (a + 1)x² + (3a + 5)x + a + 7 menyinggung sumbu x, nilai a yang memenuhi adalah..

[tex] D = b^2 - 4ac [/tex]
[tex] D = 0 [/tex]
[tex] 0 = (9a^2 + 30a + 25) - 4(a+1)(a+7) [/tex]
[tex] 0 = 9a^2 + 30a + 25 - 4a^2-32a-28 [/tex]
[tex] 0 = 5a^2 - 2a - 3 [/tex]
[tex] 0 = (5a + 3)(a - 1) [/tex]
[tex] a = -\frac{3}{5} \vee a = 1 [/tex]