Find the angles of an isosceles trapezoid if one of its angles is 70 °

Given:
ABCE – isosceles trapezoid,
angle A = 70 degrees.
Find the degree measures of the angles of the trapezoid ABCE: angle B, angle C, angle E -?
Solution:
Consider an isosceles trapezoid ABCE. Its angles at the base are equal to each other, that is, angle A = angle E = 70 degrees, angle B = angle C.
We know that the sum of the degree measures of a trapezoid is 360 degrees. Then:
angle A + angle B + angle C + angle E = 360;
70 + angle B + angle B + 70 = 360;
2 * angle B = 360 – 70;
2 * angle B = 290;
angle B = 290: 2;
angle B = 145 degrees.
Answer: 145 degrees; 145 degrees; 70 degrees.