Question

sin 70 sin 50-cos 85 cos65

Answer 1

Step-by-step explanation:

Let sin70⋅sin50−cos85⋅cos65=I

Using 2sinAsinB=cos(A+B)−cos(A−B)

2cosAcosB=cos(A−B)+cos(A+B)

We get,

I=

2

1

(cos20−cos120−cos150−cos20)

=

2

1

(−cos120−cos150)

=

2

1

(sin30+sin60)

=

2

1

(

2

1

+

2

3

)

=

4

3

+1

Answer 2

Answer:

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Step-by-step explanation:

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