A triangle needs a total of 180° to be a complete triangle. First let's solve for m∠B since we have the other angles given in that triangle.
30 + 70 = 100
180 - 100 = 80° still needed to form a complete triangle. This is what m∠B equals.
From the image provided, we can see that both triangles are the exact same. So all we need to do now is find the angle that matches m∠B. In this case that angle is m∠D. Knowing that m∠B = 80° the final answer is:
m∠D = 80°
Hoped This Helped! Good Luck!
Answer:
- The sum of the interior angles of the 15-gon

- Each interior angle of the regular polygon

Step-by-step explanation:
As we know that
In any convex polygon, if we may start at one vertex and draw the diagonals to all the other vertices, we would form triangles,
The number of triangles thus formed would always 2 LESS than the number of sides.
As
- The sum of measure of the angles of any triangle is 180°.
Thus,
The sum of the interior angles of the 15-gon will be:

Also
15-gon is regular, it means this total
is shared in equal proportion among the 15 interior angles.
And
Each interior angle of the regular polygon will be: 
Therefore, we conclude that:
- The sum of the interior angles of the 15-gon

- Each interior angle of the regular polygon

Keywords: regular polygon, 15-gon, triangle
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A line is 180 degrees so write x+(4x-20)=180