How do i find x? is the formula
"the sum of exterior angles=360°" false for concaved polygons?

  To find x you need to divide polygon into trianglesThe formula : "the sum of exterior angles=360°" is false for concaved polygons

Step-by-step explanation:

α = 180° - 135° = 45°

β = 180° - 120° = 60°

γ = 180° - 60° = 120°

δ = 180° - x

ε = 180° - 80° = 100°

If we divide the pentagon into five triangles then:

5•180° = α + β + γ + δ + ε + 4x

900° = 45° + 60° + 120° + x + 100° + 4x

900° = 325° + 5x

5x = 575°

x = 115°

60° + 120° + 135° + 80° + 115° = 510° ≠ 360°

Dis the correct  answer

Element 17 is chlorine it is a group 7 element(halogen) and belongs to period 3 of the periodic table