Question

if cosA=0.4 then find the value of cos3A​

Answer 1

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Answer 2

If cos A = 0.4 then cos 3A = - 0.944

Given :

cos A = 0.4

To find :

The value of cos 3A

Formula :

cos 3A = 4 cos³ A - 3 cos A

Solution :

Step 1 of 2 :

Write down the given value

Here it is given that cos A = 0.4

Step 2 of 2 :

Find the required value

cos 3A = 4 cos³ A - 3 cos A

⇒ cos 3A = 4 × 0.4³ - 3 × 0.4

⇒ cos 3A = 4 × 0.064 - 1.2

⇒ cos 3A = 0.256 - 1.2

⇒ cos 3A = - 0.944

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