Answer:
x = 3 and x = -7
Step-by-step explanation:
The given quadratic equation is
. We need to find the solution of this equation.
If the equation is in the form of
, then its solutions are given by :

Here, a = 1, b = 4 and c = -21
Plugging all the values in the value of x, such that :

So, the solutions of the quadratic equation are 3 and -7.
The angle immediately below x makes up the third angle of the isosceles triangle whose base angles are 55°. That third angle and x are "vertical" angles, hence equal. The value of x can be found from the sum of angles of a triangle:
x + 55° + 55° = 180°
x = 70°
The appropriate choice is the 2nd one:
70°