The value of the trigonometric expression cos θ, when (-5, -4) is a point on the terminal side of θ is -5√41/41. Hence, option D is the right choice.
What are trigonometric expressions?
Trigonometric expressions are the ratios of the sides of a right triangle, which are always constant despite the increase or decrease in the size of its sides.
These are the trigonometric ratios:
- sin θ = perpendicular/hypotenuse
- cos θ = base/hypotenuse
- tan θ = sin θ/cos θ = perpendicular/base
- cot θ = 1/tan θ = cos θ/sin θ = base/perpendicular
- sec θ = 1/cos θ = hypotenuse/base
- cosec θ = 1/sin θ = hypotenuse/perpendicular.
How to solve the question?
In the question, we are asked to find the value of cos θ, given that (-5, -4) is a point on the terminal side of θ.
This means that we; are in quadrant III. As we know, cos θ is negative in the 3rd quadrant.
The base is the distance of the x-coordinate from the origin, that is, 5 units.
The perpendicular is the distance of the y-coordinate from the origin, that is, 4 units.
By Pythagoras' Theorem,
Hypotenuse² = Base² + Perpendicular²,
or, Hypotenuse² = 5² + 4²,
or, Hypotenuse² = 25 + 16,
or, Hypotenuse = √41.
As we know, cos θ = Base/Hypotenuse = 5/√41 = 5√41/41.
Because of the 3rd quadrant, we will take, cos θ = - 5√41/41.
Thus, the value of the trigonometric expression cos θ, when (-5, -4) is a point on the terminal side of θ is -5√41/41. Hence, option D is the right choice.
Learn more about trigonometric expressions at
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