"Perimeter" is the distance all the way around the drawing. If the drawing has sides, then the perimeter is the SUM of the lengths of all the sides. It's exactly the distance an ant would have to walk along the line, to get all the way around to where he started from.
To get the perimeter of the triangle, you have to add up the lengths of the three sides.
(2a - 3) + (2a) + (3a + 1) =
2a - 3 + 2a + 3a + 1 .
Add up all the 'a's: 2a + 2a + 3a = 7a
Add up all the just plain numbers: -3 + 1 = -2
Write them together, as a binomial: 7a - 2
THAT's your expression for the perimeter.
Short Answer: y = 36°
Remark
What an interesting question!! The first thing you have to do is find out what the interior angle of a regular pentagon is. After you have done that, you can calculate y.
Method.
The exterior angles of a regular figure add up to 360°.
Step One
Find out the size of the exterior angles of a regular pentagon.
There are 5 such angles. They add up to 360°
5x = 360 Divide by 5
x = 360 / 5
x = 72°
Step Two
Find out the value of the interior angles of a pentagon.
Method
The interior and exterior angles add up to 180°
Exterior Angle + Interior Angle = 180°
Exterior angle = 72 degrees
72° + Interior Angle = 180° Subtract 72 from both sides.
Interior Angle = 180° - 72°
Interior Angle = 108°
Step Three
Solve for y.
There are 3 tiles each with an angle of 108° that are placed together. So y + 3 interior angles = 360°
y + 3*interior angles = 360°
y + 3*108 = 360
y + 324 = 360 Subtract 324 from both sides.
y = 360 - 324
y = 36°
The correct answer is y = 1/8x^2
