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Answer:
(b) 80°
Explanation:
The relevant trig relation is ...
Cos = Adjacent/Hypotenuse
The 1.5 meter distance to the wall is the side adjacent to the angle with the ground. The 9 m length of the ladder is the hypotenuse of the triangle modeling this situation.
cos(angle) = 1.5/9 = 1/6
angle = arccos(1/6) ≈ 80.4°
The angle between the ladder and the ground is about 80°.
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Additional comment
The Ladder Association recommends an angle of 75° for safety. At 80°, the ladder may have a tendency to tip the user backward.