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Case VII.

Two numbers whose product is $- 18$ , and the larger number negative, are $- 18$ and $1$ , $- 9$ and $2$ , $- 6$ and $3$ , and the sum of the last two numbers is $- 3$ . Hence, $x^{2} - 3 x - 18 = (x - 6) (x + 3) .$

Exercise 38.

Resolve into factors:

$a^{2} + 5 a + 6$ .

$a^{2} - 5 a + 6$ .

$a^{2} + 6 a + 5$ .

$a^{2} - 6 a + 5$ .

$a^{2} + 4 a - 5$ .

$a^{2} - 4 a - 5$ .

$c^{2} - 9 c + 18$ .

$c^{2} + 9 c + 18$ .

$c^{2} + 3 c - 18$ .

$c^{2} - 3 c - 18$ .

$x^{2} + 9 x + 14$ .

$x^{2} - 9 x + 14$ .

$x^{2} - 5 x - 14$ .

$x^{2} - 9 x + 20$ .

$x^{2} - x - 20$ .

$x^{2} + x - 20$ .

$x^{2} - 10 x + 21$ .

$x^{2} - 4 x - 21$ .

$x^{2} + 4 x - 21$ .

$x^{2} - 15 x + 56$ .

$x^{2} - x - 56$ .

$x^{2} - 10 x + 9$ .

$x^{2} + 13 x + 30$ .

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