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Find the value of the expression: 1+cosAsinAтАЛ+sinA1+cosAтАЛ
2cscA
2secA
2tanA
2cosA
2cscA
Substitute A=90┬░. The expression becomes 1+01тАЛ+11+0тАЛ=1+1=2. Checking the options, 2csc90┬░=2(1)=2, which matches.
An expression involving trigonometric functions of angle A: sin(A)/(1 + cos(A)) + (1 + cos(A))/sin(A).
sin2A+cos2A=1
Substitute A=90┬░. The expression becomes 1+01тАЛ+11+0тАЛ=1+1=2. Checking the options, 2csc90┬░=2(1)=2, which matches.
Students often fail to expand the numerator (1+cosA)2 correctly, missing the middle term 2cosA, or forgetting that sin2A+cos2A=1.
Taking the common denominator
To combine the fractions, multiply the denominators to get sinA(1+cosA).
sinA(1+cosA)sin2A+(1+cosA)2тАЛ
Expanding the numerator
Expand (1+cosA)2 as 1+2cosA+cos2A.
sinA(1+cosA)sin2A+1+2cosA+cos2AтАЛ
Applying trigonometric identity
Replace sin2A+cos2A with 1. The expression becomes sinA(1+cosA)1+1+2cosAтАЛ.
sinA(1+cosA)2+2cosAтАЛ=sinA(1+cosA)2(1+cosA)тАЛ
Simplifying and final result
Cancel the common term (1+cosA) from numerator and denominator to get sinA2тАЛ, which is 2cscA.
sinA2тАЛ=2cscA
A is correct because the algebraic simplification leads to 2cscA.
This type of simplification frequently appears in Calculus when evaluating integrals or derivatives of complex trigonometric functions; mastering these identities saves time.