Question

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Prove that:
2sin140°.sin20°=cos20°- 1/2

Answer 1

Answer:

To prove that cos20 + cos140 - sin10 = 0

cos 20 + cos140 - sin10

We know that cos A + cos B = 2cos ()cos ()

so by applying formula where A = 20 and B = 140

2 cos () cos () - sin10

2 cos80.cos60 - sin10

We know cos60 = 1/2

cos80 - sin10

We know cos(90-x) = sinx

cos80 - cos(90-10)

cos80- cos80

0

Hence proved.

Step-by-step explanation:

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Answer 2

Answer:

The answer already given XD