Since we want it in the form: (x - a)², let's first expand (x - a)² and then equate for the coefficients.
(x - a)² = x² - 2ax + a²
x² + 4x - 15 = x² - 2ax + a²
Now, let's focus on the middle term.
4x = -2ax
4 = -2a
a = -2
Thus, we know that a = -2
Then, we can say (x + 2)² = x² + 4x - 15
x² + 4x + 4 = x² + 4x - 15
Thus, 19 units are needed in order to complete the square to produce:
(x + 2)²
or 
At the point/angle E:
- the adjacent side(side <u>next to</u> the point/angle) is ED
- the opposite side(side of the triangle <u>across</u> from the point/angle) is DF
- the hypotenuse (the<u> longest side</u> of the triangle) is EF.
sin ∠E = 
sin ∠E = 
(simplified)
<span>By definition, lines are parallel if they have the same gradient (slope). Any horizontal line has a gradient of 0, so it is parallel to any other horizontal line</span>
