Respuesta :

Answer: A

Step-by-step explanation:

1 + cos(18x) becomes

1 + cos(9x + 9x)

1 + cos²(9x) - sin²(9x)

1 + cos²(9x) - (1 - cos²(9x))

1 + cos²(9x) - 1 + cos²(9x)

2 cos²(9x)

The 1+cos(18x) can be written as 2cos²9x after applying the trigonometric identity option (A) is correct.

What is trigonometry?

Trigonometry is a branch of mathematics that deals with the relationship between sides and angles of a right-angle triangle.

We have:

= 1 + cos(18x)

We know:

2cos²a = 1 + cos2a

We have a = 18x/2 = 9x

So,

1 + cos(18x) = 2cos²9x

Thus, the 1+cos(18x) can be written as 2cos²9x after applying the trigonometric identity option (A) is correct.

Learn more about trigonometry here:

brainly.com/question/26719838

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