? The sum of external angles is fixed at 360.
The sum of internal angles is equal to the sum of external angles, that is, the sum of internal angles is 360, and the answer is quadrilateral.
The average degree of each inner angle is 135, the column arithmetic is 135n= 180*(n-2), and the answer is octagon.
The sum of internal angles is four times that of external angles, 180*(n-2)=360*4, and the answer is a decagon.
A triangle holds, and the sum of two sides is greater than the third side.
4+4 & lt； 9,9+9 > 4, waist length 9, bottom 4, circumference 9+9+4=22cm.
∠ BCD = 3 1, then∠ ACD = 31,∠ BCA = 62.
The sum of the internal angles of a triangle is 360 degrees.
∠B= 180 -68 -62 =50
∠ADC = 180-68-3 1 = 8 1