Answer:
x = -9.7 or +5.7
Explanation:
You want the approximate solution to x² +4x = 56.
Graph
The solution is found easily by rewriting the equation to the form ...
x² +4x -56 = 0
The solution(s) will be the x-intercept(s) of the graph of x² +4x -56.
The solutions are -9.7 and +5.7.
Completing the square
We can add 4 to both sides of the equation to complete the square. (This added value is the square of half the x-coefficient.)
x² +4x +4 = 56 +4
(x +2)² = 60
x +2 = ±√60 = ±2√15
x = -2 ±2√15
x ≈ -2 ± 7.7 = -9.7, +5.7