Answer:
∠ 1 = 65°
Step-by-step explanation:
The exterior angle of a triangle is equal to the sum of the 2 opposite interior angles.
5x - 10 is an exterior angle of the triangle, then
5x - 10 = 3x + 40 ( subtract 3x from both sides )
2x - 10 = 40 ( add 10 to both sides )
2x = 50 ( divide both sides by 2 )
x = 25
The sum of the 3 angles in a triangle = 180° , so
∠ 1 + 40 + 3x = 180°
∠ 1 + 40° + 3(25) = 180°
∠ 1 + 40° + 75° = 180°
∠ 1 + 115° = 180° ( subtract 115° from both sides )
∠ 1 = 65°
