Your proof is correct and very well done
Greetings :)
To find slope of two points we will need to use this equation: 
( 6 , -12 ) ( 15 , -3 )
Now let's replace the equation with the numbers. (it will be a fraction).
= 
The equation equals 9 over 9, which also equals 1.
The slope of the line is 1.
This is an octagon, which has 8 sides.
the angle of rotation is 360/8 = 45°
<span>C.
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I think it should be 1.7?
a^2 + b^2 = c^2
c^2 = 16
Square root of 16 is 4.
1 + 3 = 4
Square root of 1 is 1 and square root of 3 is given, which is 1.7.
An equilateral has two right triangles out together, so basically that would be a rectangle.
1 x 1.7 = 1.7