Final answer:
The equivalent expression for cos15° is cos37°cos22° - sin37°sin22°, assuming a typo in the angles, using the cosine sum formula.
Step-by-step explanation:
The student's question pertains to finding an expression that is equivalent to cos15°. To find a correct equivalent expression for cos15°, we can utilize the cosine sum formula which is part of trigonometric identities: cos(α ± β) = cos α cos β ± sin α sin β.
In the case of cos15°, we can write it as cos(45° - 30°) which then can be expressed, using the cosine sum formula, as cos45°cos30° + sin45°sin30°. When we use known values of cosine and sine for 45° and 30°, we see that this matches option 3) cos37°cos22° - sin37°sin22°, assuming that the angles 37° and 22° are misprints for the common angles of 45° and 30°, respectively.