Question

Cos*2(10)+cos*2(20)+cos*2(30)+cos*2(40)+cos*2(50)+cos*2(60)+cos*2(70)+cos*2(80)=_____

Answer 1

Step-by-step explanation:

sin

2

60°+cos

2

60°=(

2

3

)

2

+(

2

1

)

2

⇒

4

3

+

4

1

=

4

4

=1

∴sin

2

45°+cos

2

45°=(

2

1

)

2

+(

2

1

)

2

=

2

1

+

2

1

=1

∴sin

2

60°+cos

2

60°=sin

2

45°+cos

2

45°

Hence, the answer is sin

2

45°+cos

2

45°.