cos⁴x - sin⁴x ÷ 1 - tan x = (cot x + 1) ÷ sec x cosec x
We can start by simplifying the left-hand side of the equation:
cos⁴x - sin⁴x ÷ 1 - tan x
= (cos²x + sin²x)(cos²x - sin²x) ÷ (cos x / sin x)
= (cos²x - sin²x)(cos²x + sin²x) ÷ (cos x / sin x)
= (cos²x - sin²x)(1) ÷ (cos x / sin x)
= cos²x - sin²x ÷ (cos x / sin x)
= (cos x / sin x)(cos²x - sin²x) ÷ (cos x / sin x)
= cos²x - sin²x
Now, let's simplify the right-hand side of the equation:
(cot x + 1) ÷ sec x cosec x
= (cos x / sin x + 1) ÷ (1 / (cos x sin x))
= (cos x + sin x) ÷ (sin x cos x)
= cos x / cos x sin x + sin x / cos x sin x
= (cos x + sin x) ÷ sin x cos x
= (cos²x + sin²x + 2sinxcosx) ÷ sin x cos x
= (1 + 2sinxcosx) ÷ sin x cos x
Now, we can see that the left-hand side of the equation is equal to cos²x - sin²x, which is also equal to (cos x + sin x)(cos x - sin x).
We can rewrite the right-hand side of the equation as (1 + 2sinxcosx) ÷ sin x cos x = (sin²x + cos²x + 2sinxcosx) ÷ sin x cos x = (sin x + cos x)² ÷ sin x cos x.
So, the equation becomes:
(cos x + sin x)(cos x - sin x) = (sin x + cos x)² ÷ sin x cos x
Dividing both sides by sin x cos x, we get:
(cos x + sin x)(cos x - sin x) ÷ sin x cos x =
(cos x + sin x)(cos x - sin x) ÷ sin x cos x = (sin x + cos x)² ÷ sin x cos x
= (cos²x - sin²x) ÷ sin x cos x + 2(cos x + sin x) ÷ sin x cos x
= (cos²x ÷ sin x cos x) - (sin²x ÷ sin x cos x) + 2(cos x ÷ sin x cos x) + 2(sin x ÷ sin x cos x)
= (cos x ÷ sin x) - (sin x ÷ cos x) + 2(cosec x + cot x)
= cot x + cosec x - tan x - sec x + 2(cosec x + cot x)
Answers & Comments
To prove the given trigonometric identity, we'll start by expressing all trigonometric functions in terms of sin(x) and cos(x):
1. cos^4(x) - sin^4(x) = (cos^2(x) + sin^2(x))(cos^2(x) - sin^2(x)) = cos^2(x) - sin^2(x) ... (1)
2. 1 - tan(x) = (cos^2(x) + sin^2(x)) - (sin^2(x) / cos^2(x)) = (cos^2(x) + sin^2(x)) - sin^2(x) / cos^2(x) ... (2)
3. cot(x) = cos(x) / sin(x)
4. sec(x) = 1 / cos(x)
5. cosec(x) = 1 / sin(x)
Now, let's simplify the right-hand side of the identity:
(cot(x) + 1) / (sec(x) cosec(x)) = (cos(x) / sin(x) + 1) / (1 / cos(x) * 1 / sin(x)) = (cos(x) + sin(x)) / (1 / (cos(x) sin(x)))
Next, let's rationalize the denominator:
(cot(x) + 1) / (sec(x) cosec(x)) = (cos(x) + sin(x)) / (1 / (cos(x) sin(x))) * (cos(x) sin(x) / cos(x) sin(x))
= (cos(x) + sin(x)) * (cos(x) sin(x))
= cos(x) sin(x) + sin^2(x) cos(x)
Now, let's express sin^2(x) in terms of cos^2(x) using the Pythagorean identity: sin^2(x) = 1 - cos^2(x)
(cot(x) + 1) / (sec(x) cosec(x)) = cos(x) sin(x) + (1 - cos^2(x)) cos(x)
(cot(x) + 1) / (sec(x) cosec(x)) = cos(x) sin(x) + cos(x) - cos^3(x)
Finally, let's express cos^3(x) in terms of cos(x) using the identity: cos^3(x) = cos(x) * cos^2(x)
(cot(x) + 1) / (sec(x) cosec(x)) = cos(x) sin(x) + cos(x) - cos(x) * cos^2(x)
Now, let's simplify the left-hand side of the identity using equation (1) and equation (2):
cos^2(x) - sin^2(x) / (1 - tan(x)) = cos^2(x) - sin^2(x) / (cos^2(x) + sin^2(x) - sin^2(x) / cos^2(x))
= cos^2(x) - sin^2(x) / (cos^2(x) + (cos^2(x) * sin^2(x)) / cos^2(x))
= cos^2(x) - sin^2(x) / (cos^2(x) + cos^2(x) * sin^2(x))
= cos^2(x) - sin^2(x) / (cos^2(x) * (1 + sin^2(x)))
= (cos^2(x) - sin^2(x)) / (cos^2(x) * (1 + sin^2(x)))
Now, let's use the Pythagorean identity: cos^2(x) = 1 - sin^2(x)
cos^2(x) - sin^2(x) / (1 - tan(x)) = (1 - sin^2(x) - sin^2(x)) / ((1 - sin^2(x)) * (1 + sin^2(x)))
= (1 - 2sin^2(x)) / (1 - sin^4(x))
Now, let's express sin^4(x) in terms of sin^2(x):
sin^4(x) = (sin^2(x))^2 = (sin^2(x)) * (sin^2(x)) = sin^2(x) * sin^2(x)
cos^2(x) - sin^2(x) / (1 - tan(x)) = (1 - 2sin^2(x)) / (1 - sin^2(x) * sin^2(x))
Now, let's express 1 - 2sin^2(x) in terms of cos^2(x):
1 - 2sin^2(x) = cos^2(x) - 2sin^2(x) * cos^2(x) = cos^2(x) - 2sin^2(x) * (1 - sin^2(x)) = cos^2(x) - 2sin^2(x) + 2sin^2(x) * sin^2(x) = cos^2(x) - 2sin^2(x) + 2sin^4(x)
cos^2(x) - sin^2(x) / (1 - tan(x)) = (cos^2(x) - 2sin^2(x) + 2sin^4(x)) / (1 - sin^2(x) * sin^2(x))
Now, let's use the Pythagorean identity: cos^2(x) = 1 - sin^2(x)
cos^2(x) - sin^2(x) / (1 - tan(x)) = (1 - sin^2(x) - 2sin^2(x) + 2sin^4(x)) / (1 - sin^2(x) * sin^2(x))
= (1 - 3sin^2(x) + 2sin^4(x)) / (1 - sin^4(x))
Finally, let's factor the numerator:
cos^2(x) - sin^2(x) / (1 - tan(x)) = (1 - sin^2(x))(1 - 2sin^2(x)) / (1 - sin^4(x))
Now, using the identity: 1 - 2sin^2(x) = cos^2(x)
cos^2(x) - sin^2(x) / (1 - tan(x)) = (1 - sin^2(x))(cos^2(x)) / (1 - sin^4(x))
Using the identity: 1 - sin^2(x) = cos^2(x)
cos^2(x) - sin^2(x) / (1 - tan(x)) = (cos^2(x) * cos^2(x)) / (1 - sin^4(x))
Dividing both sides by (1 - sin^4(x)):
cos^2(x) - sin^2(x) / (1 - tan(x)) = cos^2(x) / (1 - sin^4(x))
Now, let's use the Pythagorean identity: 1 - sin^2(x) = cos^2(x)
cos^2(x) - sin^2(x) / (1 - tan(x)) = cos^2(x) / cos^2(x)
cos^2(x) - sin^2(x) / (1 - tan(x)) = 1
This proves
cos⁴x - sin⁴x ÷ 1 - tan x = (cot x + 1) ÷ sec x cosec x
We can start by simplifying the left-hand side of the equation:
cos⁴x - sin⁴x ÷ 1 - tan x
= (cos²x + sin²x)(cos²x - sin²x) ÷ (cos x / sin x)
= (cos²x - sin²x)(cos²x + sin²x) ÷ (cos x / sin x)
= (cos²x - sin²x)(1) ÷ (cos x / sin x)
= cos²x - sin²x ÷ (cos x / sin x)
= (cos x / sin x)(cos²x - sin²x) ÷ (cos x / sin x)
= cos²x - sin²x
Now, let's simplify the right-hand side of the equation:
(cot x + 1) ÷ sec x cosec x
= (cos x / sin x + 1) ÷ (1 / (cos x sin x))
= (cos x + sin x) ÷ (sin x cos x)
= cos x / cos x sin x + sin x / cos x sin x
= (cos x + sin x) ÷ sin x cos x
= (cos²x + sin²x + 2sinxcosx) ÷ sin x cos x
= (1 + 2sinxcosx) ÷ sin x cos x
Now, we can see that the left-hand side of the equation is equal to cos²x - sin²x, which is also equal to (cos x + sin x)(cos x - sin x).
We can rewrite the right-hand side of the equation as (1 + 2sinxcosx) ÷ sin x cos x = (sin²x + cos²x + 2sinxcosx) ÷ sin x cos x = (sin x + cos x)² ÷ sin x cos x.
So, the equation becomes:
(cos x + sin x)(cos x - sin x) = (sin x + cos x)² ÷ sin x cos x
Dividing both sides by sin x cos x, we get:
(cos x + sin x)(cos x - sin x) ÷ sin x cos x =
(cos x + sin x)(cos x - sin x) ÷ sin x cos x = (sin x + cos x)² ÷ sin x cos x
= (cos²x - sin²x) ÷ sin x cos x + 2(cos x + sin x) ÷ sin x cos x
= (cos²x ÷ sin x cos x) - (sin²x ÷ sin x cos x) + 2(cos x ÷ sin x cos x) + 2(sin x ÷ sin x cos x)
= (cos x ÷ sin x) - (sin x ÷ cos x) + 2(cosec x + cot x)
= cot x + cosec x - tan x - sec x + 2(cosec x + cot x)
= 3cosec x + 2cot x - sec x - tan x