Answer:
50.0°
Explanation:
In the diagram below, line AD represents the plank and line BC represents the wall.
θ is the angle the plank makes with the wall.
Length of the plank on the wall
The plank is 4 m long and 1.2 m extends beyond the wall.
The length of the plank resting on the wall is
AB = 4 – 1.2
AB = 2.8 m
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Angle with the wall
Triangle ABC is a right triangle, because the wall is perpendicular to the ground.
cosθ = BC/AB
BC = 1.8 m; AB = 2.8
cosθ = 1.8/2.8
θ = cos⁻¹(1.8/2.8)
θ = cos⁻¹(0.6429)
θ = 50.0°
The plank makes an angle of 50.0° with the wall.