Question

sec 3x = -2 general solution?​

Answer 1

Answer:

Answer

Correct option is

A

True

Given

cosx+cos3x+⋯+cosnx=

2sinx

sin2

n

x

LHS

cosx+cos3x+⋯+cosnx

Multipying and dividing by 2sinx

2sinx

2sinxcosx

+cos3x+⋯+cosnx

2sinx

sin2x

+cos3x+⋯+cosnx

2sinx

sin2x+2sinxcos3x

+⋯+cosnx

2sinx

sin2x+sin4x−sin2x

+⋯+cosnx

2sinx

sin4x

+cos5x+⋯+cosnx

⟹

2sinx

sin2

n−1

x

+cosnx

⟹

2sinx

sin2

n−1

x+2sinxcosnx

⟹

2sinx

sin2

n−1

x+sin2

n

x−sin2

n−1

x

⟹

sinx

sin2

n

x

RHS

Hence proved