He made a mistake in step #2. It seemed to be a trivial mistake because it involved signs, but it still had a great impact. Since step#2, his solution was already wrong.
Instead of
(-1)²-4(2)(-6) = 1 + 48 = 49
What he did is
(-1)²-4(2)(-6) = -1 + 48 = 47
To find the area of the shaded region you need find the area
of the shaded region and subtract the area of the unshaded region.
Area of a rectangle = width x length
A = (x + 10) x (2x + 5)
Next apply FOIL or
First Outer Inner Last
A = (x * 2x) (x * 5) (10 * 2x) (10 * 5)
A= 2x2 + 5x + 20x + 50
A= 2x2 +25x +50
Area of a square= sides2
A= (x + 1)2
A= (x+1) (x+1)
Next apply FOIL or
First Outer Inner Last
A = (x *x) (1*x) (1*x) (1*1)
A = x2 + 1x + 1x +1
A= x2 + 2x +1
A= 2x2 +25x +50 - 2x2 +25x +50
A= 50x + 100
the angle 4pi/5 in quadrent 2
