Answer:
alpha = 21°
Step-by-step explanation:
You see that this rectangle has four right angles, meaning each of 90 °
That is why it is called a rectangle in the first place. ( The 'rec' in rectangle stands for 'right' or 'streight' and it indicates all angles in the rectangle being 90 °).
Anyway, corner alpha added with the given angle of 69 ° must there fore add up to the value of a streight corner, right?
apha + 69 = 90
alpha = 90 - 69
alpha = 21°
