Only thing I can tell you is to use a corner to a piece of paper. The corner is 90 degrees. It's acute if the corner is bigger than the angle. Obtuse if its smaller.
In the given figure above, we can use the formula for tangent-tangent angle. This is under the type of angle whose vertex is outside the circle and its sides intersects the circle.
Applying the tangent-tangent angle formula:
m∠APB =

(ALB - AB)
m∠APB = angle of the vertex
ALB = measure of arc ALB
AB = measure of arc AB
we all know that the total measure of arc is equal to 360, hence, ALB + AB = 360
let: x = measure of arc AB
360 - x = measure of arc ALB
substitute:
78 =

{(360 - x) - x}
78 =

(360 - 2x)
78 = 180 - x ⇒ simplifying further by dividing both 360 and -2x by 2
x = 180 - 78 ⇒ combining like terms
x = 102
arc AB = 102 ⇒ Answer
Answer:
Consider the angle Ф.
the line opposite to Ф is the perpendicular -> PQ = 5cm
The base is the line with whom the perpendicular has 90° angle -> PR = 12cm
Finally, hypotenuse is the line opposite to the 90° which is QR= 13cm
Answer: 12 for accurate 12.4
Step-by-step explanation: This is easy all you needed to do was divide 9,674.48 by 780.20 and get 12.4