Question

Solve 3x2 + 18x + 15 = 0 by completing the square

Answer 1

Step 1

Given;

`3x^2+18x+15=0`

Required; To solve by completing the square method.

Step 2

Subtract 15 from both sides of the equation.

`\begin{gathered} 3x^2+18x+15-15=0-15 \\ 3x^2+18x=-15 \end{gathered}`
`\begin{gathered} Divide\text{ all terms by 3} \\ x^2+6x=-5 \end{gathered}`

Find half of the coefficient of x (i.e 6) and square it

`((6)/(2))^2=3^2`

Add it to both sides

`\begin{gathered} x=\pm2-3 \\ x=-1\text{ or -5} \end{gathered}`

Answer;

`x=-1,-5`