Prove that  sinA/(1+cosA) + (1+cosA)/sinA = 2/sinA

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lfryerda's profile pic

lfryerda | High School Teacher | (Level 2) Educator

Posted on

To prove a trigonometric identity, you need to start from one side of the identity and, using standard formulas, change it to the other side of the identity.  Generally, you start from the side that is more complicated.

`LS = sinA/(1+cosA)+(1+cosA)/sinA`   find common denominator

`={sin^2A+(1+cosA)^2}/{sinA(1+cosA)}`   simplify numerator

`={sin^2A+1+2cosA+cos^2A}/{sinA(1+cosA)}`

`={2+2cosA}/{sinA(1+cosA)}`  factor numerator

`={2(1+cosA)}/{sinA(1+cosA)}`   cancel common factor

`=2/sinA`

`=RS`

The identity has been proven.

karnishekhawat's profile pic

karnishekhawat | (Level 1) eNoter

Posted on

Sin A/(1+cosA) + (1+cosA)/sinA

= sin^2 A +(1+cosA)^2 /sinA(1+cosA)

=sin^2 A + 1+cos^2 A+2 cos A / sin A (1+cos A)

=2+2 Cos A/sinA(1+cos A)

=2(1+cos A)/sin A (1+cos A)

= 2/sin A

Hence proved

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