Question

Show so that the expression of cos4A in term of SinA is 8Sin^4 - 8Sin^2A + 1​

Answer 1

Answer:

Step-by-step explanation:

L

H

S

=

cos

4

x

=

2

cos

2

(

2

x

)

−

1

=

2

(

cos

(

2

x

)

)

2

−

1

=

2

(

2

cos

2

x

−

1

)

2

−

1

=

2

(

4

cos

4

x

−

4

cos

2

x

+

1

)

−

1

=

8

cos

4

x

−

8

cos

2

x

+

2

−

1

=

8

cos

4

x

−

8

cos

2

x

+

1

=

R

H

S

Again

L

H

S

=

cos

4

x

=

2

cos

2

(

2

x

)

−

1

=

2

(

1

−

2

sin

2

x

)

)

2

−

1

=

2

(

1

−

4

sin

2

x

+

4

sin

4

x

)

−

1

=

2

−

8

sin

2

x

+

8

sin

4

x

−

1

=

8

sin

4

x

−

8

sin

2

x

+

1

=

R

H

S

sin

2

x

+

cos

2

x

=

1

cos

2

x

=

1

−

sin

2

x

substitute in the equation as follows

8

cos

4

x

−

8

cos

2

x

+

1

=

8

cos

2

x

(

cos

2

x

−

1

)

+

1

=

8

(

1

−

sin

2

x

)

(

1

−

sin

2

x

−

1

)

+

1

=

8

(

1

−

sin

2

x

)

(

−

sin

2

x

)

+

1

=

8

sin

4

x

−

8

sin

2

x

+

1