Final answer:
To solve the equation cos(5x+15) = sin(4x-15), set the arguments equal to each other and solve for x.
Step-by-step explanation:
To solve the equation cos(5x+15) = sin(4x-15), we can use the trigonometric identity sin(a) = cos(90-a). Therefore, we have cos(5x+15) = cos(90-(4x-15)). Setting the arguments equal to each other, we have 5x+15 = 90-(4x-15). Solving for x, we get x = 10. Therefore, the value of x is B. x = 10.