Find the value of sin73° + cos137°

sin73° + cos137° [(cos90°+θ) = -sinθ] 

= sin73° + (-sin47°)      [sin(c-d) = 2cos\(\frac{c+d}{2}\) × sin\(\frac{c - d}{2}\)]

⇒ 2cos(\(\frac{73+47}{2}\)) × sin(\(\frac{73 - 47}{2}\))

2 × cos60° × sin13°

2 × \(\frac{1}{2}\) × sin13°

= sin13°