Answer:
72°
Step-by-step explanation:
From the figure given, angle D intercepts arc ABC. According to the Inscribed Angle Theorem:
m < D = ½(ABC) = ½(AB + BC)
Thus,
[tex] 56 = \frac{1}{2}(AB + 40) [/tex]
Solve for AB
[tex] 56 = \frac{AB + 40}{2} [/tex]
Multiply both sides by 2
[tex] 56*2 = \frac{AB + 40}{2}*2 [/tex]
[tex] 112 = AB + 40 [/tex]
Subtract both sides by 40
[tex] 112 - 40 = AB + 40 - 40 [/tex]
[tex] 72 = AB [/tex]
Arc AB = 72°
