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Simplify the expression: 1+sinθ1−sinθ
secθ−tanθ
secθ+tanθ
tanθ−secθ
cosθ−sinθ
secθ−tanθ
Plug in a simple value like θ=0°. The expression becomes 1/1=1. Evaluating the options at θ=0°: (A) sec0−tan0=1−0=1. This matches.
An expression containing a square root of a ratio involving sine functions: 1+sinθ1−sinθ
1+sinθ1−sinθ=cosθ1−sinθ
Plug in a simple value like θ=0°. The expression becomes 1/1=1. Evaluating the options at θ=0°: (A) sec0−tan0=1−0=1. This matches.
Many students forget to split the fraction cosθ1−cosθsinθ into secθ−tanθ and mistakenly stop at the intermediate step.
Rationalize the denominator
Multiply the numerator and denominator inside the square root by the conjugate (1−sinθ).
(1+sinθ)(1−sinθ)(1−sinθ)(1−sinθ)=1−sin2θ(1−sinθ)2
Use trigonometric identity
Apply the identity 1−sin2θ=cos2θ to simplify the denominator.
cos2θ(1−sinθ)2=cosθ1−sinθ
Simplify and separate
Divide each term in the numerator by the denominator cosθ using the definitions of secθ and tanθ.
cosθ1−cosθsinθ=secθ−tanθ
A is correct because rationalizing the denominator and applying the identity cos2θ=1−sin2θ results in secθ−tanθ.
The technique of multiplying by the conjugate is frequently used in limit problems involving square roots in Calculus and in simplifying complex surds in Algebra.