The correct answer from each drop-down menu is:
If cost 8 = 8 and tan20 = 17, then cos28 = -8/17.
To solve this problem, we can use the double angle formula for cosine:
cos2θ = 2cos²θ - 1
We know that cos20 = 17, so we can substitute this value into the formula:
cos2(20°) = 2(cos20°)² - 1
cos2(20°) = 2(17²)² - 1
cos2(20°) = -8/17
Therefore, the correct answer is cos28 = -8/17.