With some simple rearrangement, we can rewrite the numerator as

Then factorizing the difference of squares,
, we end up with

Answer:
1+0
Step-by-step explanation:
because your adding
Since the three angles of a triangle add to give 180°
The the size of the largest angle 4 = 180° ×

= 180° ×
∴ the size of the largest angle = 80°