Question

Hellllllppppppp! Thank You :)
What are the solutions of 3x2 + 15 = -6x?

-1 ± i

-1 ± 2i

-2 ± i

-2 ± 2i

Answer 1

My Answer Is A

Answer 2

@phi

Answer 3

First put your equation into standard form
3x2 + 15 = -6x

add 6x to both sides to get
\[ 3x^2 + 6x + 15 = 0 \]
notice that each term can be divided by 3. Do that to simplify. (in other words, divide both sides of the equation by 3)
\[ x^2 +2x + 5 =0 \]

now use quadratic formula
see http://www.khanacademy.org/math/algebra/quadratics/quadratic_formula/v/using-the-quadratic-formula

or "complete the square"

Answer 4

Though a bit painful, you could check each of the choices and see which one works.

You chose -1 ± i
Let's check -1 + i
Let x= -1 + i. x^2 = (-1+i)(-1+i)= 1 -2i + i^2 = 1 -2i-1 = -2i

put those values in the simplified version of the equation
\[ x^2+2x+5=0 \\ -2i +2(-1+i)+5 \\ -2i -2+2i +5 = -2+5 = 3\]
3 is not 0, so A is not the answer.