Answer:
 θ ≈ 0.785398 -1.089533i radians
Explanation:
The sum of the sine and cosine can never exceed √2 for real-valued angles. The angle that gives this sum is the complex angle ...
 θ ≈ 0.785398 -1.089533i radians
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Additional comment
 sin(θ) +cos(θ) = √2·cos(θ-π/4)
We want the value of this to be 2.34, so ...
 2.34 = √2·cos(θ -π/4)
 cos(θ -π/4) = 2.34/√2
 θ -π/4 = arccos(1.17√2)
 θ = π/4 +arccos(1.17√2)
A suitable calculator can provide the complex value of the arccos of a number greater than 1.