cos155° = _____-cos25°cos(-25)°cos 55°

To solve the equation cos155° = _____-cos25°cos(-25)°cos 55°, we can break it down step by step:

Step 1: Evaluate cos25°cos(-25)°cos 55°

• First, calculate cos25°: Use a calculator or reference table to find the cosine of 25 degrees. Let's say it is equal to x.
• Next, calculate cos(-25)°: The cosine of a negative angle is the same as the cosine of its positive counterpart. So, cos(-25)° is also equal to x.
• Finally, calculate cos 55°: Use a calculator or reference table to find the cosine of 55 degrees. Let's say it is equal to y.
• Multiply these values together: x * x * y = x^2 * y.

Step 2: Substitute the value from step 1 into the equation

• Replace the expression cos25°cos(-25)°cos 55° with x^2 * y in the original equation: cos155° = _____ - x^2 * y.

Step 3: Evaluate cos155°

• Use a calculator or reference table to find the cosine of 155 degrees. Let's say it is equal to z.

Step 4: Substitute the value from step 3 into the equation

• Replace the blank space in the equation cos155° = _____ - x^2 * y with z: cos155° = z - x^2 * y.

Now, you have the equation cos155° = z - x^2 * y.