If 0° < theta < 90° and sin theta + cos theta = a, then the value of tan theta + cot theta is
a) a² + 1
b) 1/(a²+2)
c) 2/(a²-1)
d) 4/(a²-1)
Please show the full calculation.
Answers
Given that:
- 0° < θ < 90° and sin θ + cos θ = a
To Find:
- The value of tan θ + cot θ.
According to the question.
↠ sin θ + cos θ = a ______(i)
Squaring both sides.
↠ (sin θ + cos θ)² = a²
Using (a + b)² = a² + b² + 2ab
↠ sin²θ + cos²θ + 2sin θ•cos θ = a²
Value of sin²θ + cos²θ = 1
↠ 1 + 2sin θ•cos θ = a²
↠ 2sin θ•cos θ = a² - 1
↠ sin θ•cos θ = (a² - 1)/2 ______(ii)
Again,
↠ sin θ + cos θ = a
Dividing by cos θ both sides.
↠ sin θ/cos θ + cos θ/cos θ = a/cos θ
↠ tan θ + 1 = a/cos θ ______(iii)
Again,
↠ sin θ + cos θ = a
Dividing by sin θ both sides.
↠ sin θ/sin θ + cos θ/sin θ = a/sin θ
↠ 1 + cot θ = a/sin θ ______(iv)
Adding eqⁿ (iii) and eqⁿ (iv).
↠ tan θ + 1 + 1 + cot θ = a/cos θ + a/sin θ
↠ tan θ + cot θ = {a/cos θ + a/sin θ} - 2
↠ tan θ + cot θ = {(asin θ + acos θ)/sin θ•cos θ} - 2
↠ tan θ + cot θ = {a(sin θ + cos θ)/sin θ•cos θ} - 2
Putting all the values.
↠ tan θ + cot θ = {a(a)/(a² - 1)/2} - 2
↠ tan θ + cot θ = {2a²/(a² - 1)} - 2
↠ tan θ + cot θ = (2a² - 2a² + 2)/(a² - 1)
↠ tan θ + cot θ = 2/(a² - 1)
Hence,
- The value of tan θ + cot θ is c) 2/(a²-1).
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Step-by-step explanation:
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