Question

Which is the set of roots for the equation? x2 + 3x - 18 = 0
A. {18,-1}
B. {-6,3}
C. {-2,9}
D. {9} Which is the set of roots for the equation? x2 + 3x - 18 = 0
A. {18,-1}
B. {-6,3}
C. {-2,9}
D. {9} @Mathematics

Answer 1

B

Answer 2

yup b is correct

Answer 3

Use the quadratic formula: \[(-b \pm \sqrt{b^{2}-4ac})\div2a\]
To find the roots for a quadratic, to the form of \[ax^{2} + bx + c\]
In this case, a = 1, b = 3 and c = -18 thus:
\[(-3\pm \sqrt{3^{2}-4(1\times18)})\div(2\times1)\]
\[=(-3\pm \sqrt{9-(-72)})\div2\]
\[=(-3\pm9)\div2\]

Answer 4

Another way to look at this problem is by generating factors. -18 = -(6 * 3). To get +3x, you need 6 to be positive and 3 to be negative. So, the factors are (x+6)(x-3). This equation is zero if x = -6 or x = 3.