Question

Prove that sec2θ - [sin2θ-sin4θ] / [2cos4θ-cos2θ] =1

Answer 1

Answer:

Let a, b, c be lengths of right angled triangle

By definition

sinθ=b/c(

hypotenuse

opposite side

)

cosθ=a/c(

hypotenuse

adjacent side

)

sin

2

θ+cos

2

θ=

c

2

b

2

+

c

2

a

2

=

c

2

a

2

+b

2

From Pythagoras theorem

c

2

=a

2

+b

2

∴

c

2

a

2

+b

2

=1

sin

2

θ+cos

2

θ=1

Hence, proved.