In △ ABC, the degrees of a and B are as follows, and () A. ∠A=50°，∠B=70°B. ∠A=70°，∠B=40°C. ∠A=30°，∠B=90°D. ∠A=80°，∠B=60°

In △ ABC, the degrees of a and B are as follows, and () A. ∠A=50°，∠B=70°B. ∠A=70°，∠B=40°C. ∠A=30°，∠B=90°D. ∠A=80°，∠B=60°

When the top angle is ∠ a = 50 °, B = 65 °, when the top angle is ∠ B = 70 °, a = 55 ° so option a is wrong. When the top angle is ∠ B = 40 °, a = 70 ° so option B is correct. When the top angle is ∠ a = 30 °, B = 75 °, when the top angle is ∠ B = 90 °, a = 45 ° so option C is wrong. When the top angle is ∠ a = 80 °, B = 50 ° and when the top angle is ∠ B = 60 °, a = 60 ° so option D Wrong. So choose B

It is known that △ ABC is an isosceles triangle, and ∠ a + B = 130 ° to find the degree of ∠ a?

Angle c = 50 degrees, angle a = 50 degrees. B = 80 degrees or a = 80 degrees, B = 50 degrees

In the RT triangle ABC, AC = BC, P is a point in the triangle, and PA = 1, Pb = 3, PC = 2, find the degree of angle APC

Rotate the triangle APC 90 ° anticlockwise so that the triangles CQB, B and a coincide
Then the triangle CQP is isosceles right triangle, angle CPQ = CQP = 45 °, PQ = 2 times root 2
In triangle pqb, the angle pqb = 90 ° is obtained by Pythagorean theorem