The sum of the internal angles of the triangle is 180, and the right angle is 90, ∠1= 70.

Subtract the right angle from the sum of the internal angles of a triangle, and then subtract ∠ 1.

Formula:180-90-70 = 20; Available: 2 = 20.

Extended data:

A triangle divided by an angle

Judgment method 1:

1, acute triangle: all three internal angles of the triangle are less than 90 degrees.

2. Right triangle: One of the three internal angles of the triangle is equal to 90 degrees, which can be recorded as Rt△.

3. obtuse triangle: one of the three internal angles of the triangle is greater than 90 degrees.

Decision method 2:

1, acute triangle: the largest of the three internal angles of a triangle is less than 90 degrees.

2. Right triangle: The largest of the three internal angles of a triangle is equal to 90 degrees.

3. obtuse triangle: the largest of the three internal angles of a triangle is greater than 90 degrees and less than 180 degrees.

Among them, acute triangle and obtuse triangle are collectively called oblique triangle.