Question

cot20°cot40° + cot40° cot80° - cot80° cot20° is equal to :
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Answer 1

Answer:

Correct option is

B

tan50

∘

k=

cot80

+cot20

3+cot80

cot20

=

cot(90

−10

)+cot(90

−70

)

3+cot(90

−10

)cot(90

−70

)

⇒k=

tan10

+tan70

3+tan10

tan70

⇒k=

sin10

cos70

+cos10

sin70

3cos10

cos70

+sin70

sin10

⇒k=

sin(10

+70

)

3(

2

cos(10

+70

)+cos(10

−70

)

)+(

2

cos(10

−70

)−cos(10

+70

)

)

⇒k=

sin80

2cos60

+cos80

=

sin80

1+cos80

⇒k=

2sin40

cos40

2cos

2

40

=cot40

=tan50

o

Answer 2

cot(20×40+40×80-80×20)=?

cot 2400=?

cot=1/2400