Respuesta :
1. It is proven that (cos³θ + sin³θ)/(sinθ + cosθ) = 1 - sinθscosθ
2. It is proven that (cosecθsecθ)² - (1 - tan²θ)²/tan²θ = 4
1. How to prove the trigonometric expression?
(cos³θ + sin³θ)/(sinθ + cosθ) = 1 - sinθ + cosθ
We need to show that L.H.S = R.H.S
(cos³θ + sin³θ)/(sinθ + cosθ)
Using the sum of two cubes, we have x³ + y³ = (x + y)(x² - xy + y²)
So, (cos³θ + sin³θ) = (cosθ + sinθ)(cosθ² - cosθsinθ + sinθ²)
= (cosθ + sinθ)(cosθ² + sinθ² - cosθsinθ)
= (cosθ + sinθ)(1 - cosθsinθ)
So, (cos³θ + sin³θ)/(sinθ + cosθ) = (cosθ + sinθ)(1 - cosθsinθ)/(sinθ + cosθ)
= 1 - sinθscosθ
Thus, it is proven that (cos³θ + sin³θ)/(sinθ + cosθ) = 1 - sinθscosθ
2. How to prove the trigonometric expression?
(cosecθsecθ)² - (1 - tan²θ)²/tan²θ = 4
WE need to show that L.H.S = R.H.S
(cosecθsecθ)² - (1 - tan²θ)²/tan²θ = (1/sinθcosθ)² - (1 - 2tan²θ + tan⁴θ)/tan²θ
= (1/sinθcosθ)² - 1/tan²θ + 2tan²θ/tan²θ - tan⁴θ/tan²θ
= (1/sinθcosθ)² - 1/tan²θ + 2 - tan²θ
= [(1 - (sinθcosθ)²/tan²θ + 2(sinθcosθ)² - (sinθcosθ)²tan²θ]/(sinθcosθ)²
= [(1 - (sinθcosθ)²cos²θ/sin²θ + 2(sinθcosθ)² - (sinθcosθ)²sin²θ/cos²θ]/(sinθcosθ)²
= [(1 - cos⁴θ + 2(sinθcosθ)² - sin⁴θ]/(sinθcosθ)²
= [(1 - (cos⁴θ + sin⁴θ) + 2(sinθcosθ)² ]/(sinθcosθ)²
Since (cos⁴θ + sin⁴θ = (cos²θ)² + (sin²θ)²
Using the sum of two squares a² + b² = (a + b)² - 2ab
(cos²θ)² + (sin²θ)² = (cos²θ + sin²θ)² - 2cos²θsin²θ = 1 - 2cos²θsin²θ (Since cos²θ + sin²θ = 1)
So, (cosecθsecθ)² - (1 - tan²θ)²/tan²θ = [(1 - (cos⁴θ + sin⁴θ) + 2(sinθcosθ)² ]/(sinθcosθ)²
= [(1 - (1 - 2cos²θsin²θ) + 2(sinθcosθ)² ]/(sinθcosθ)²
= [(1 - 1 + 2cos²θsin²θ + 2(sinθcosθ)² ]/(sinθcosθ)²
= [0 + 4(sinθcosθ)² ]/(sinθcosθ)²
= 4(sinθcosθ)² ]/(sinθcosθ)²
= 4
So, it is proven that (cosecθsecθ)² - (1 - tan²θ)²/tan²θ = 4
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