The value of x is 35°.
The sine and cosine functions are complementary functions, which means that sin(90° - x) = cos(x) and cos(90° - x) = sin(x).
The sine and cosine functions are even functions, which means that sin(-x) = -sin(x) and cos(-x) = cos(x).
The sum of the squares of the sine and cosine functions is equal to 1, which means that sin²(x) + cos²(x) = 1.
Using these properties, we can solve for the value of x in the equation sin(55°) = cos(x).
Since sin(55°) = cos(35°),
we know that x must be equal to 35°.
This is because sin(55°) and cos(35°) are complementary functions, which means that they are equal to each other.