Answer:
Step-by-step explanation:
The given sequence is
-12,-16,-20...
The first term of this sequence is 
.
The common difference is
The nth term of this arithmetic sequence is;
We substitute the values for the first term and the common difference to obtain;
x=0 or x=4
just factorize basically
cancels the x’s so it’d be 3x-12=0 and from that x=4
Keeping in mind that the area of a rectangle is simply width * length, if we get the area of the larger rectangle, and then
subtract the area of the smaller rectangle, we're in effect making a hole in the larger rectangle's area and thus what's leftover is the shaded area.
Angle a is directly opposite from a 40 degree angle, so a=40. Then we can find b since the sum of the angles of all triangles is 180 and there is a right angle in there along with angle a:
Last, to find c we just notice that it is supplementary with an angle of measure 65, so:
So our angles are a=40, b=50, c=115.
