Two circles touch each other externally at point P in the given figure. AB is the direct common tangent of these circles. Then ÐAPB equals to:
90°
AM = MP [tangents from an external point]
∠MAP = ∠MPA
Similarly, MP = MB
∠MBP = ∠MPB
Now in ∠ABP
∠PAB + ∠ABP + ∠APB =180∘
∠MPA +∠MPB +∠MPA +∠MPB = 180∘
∠MPA +∠MPB = 90∘
So, ∠APB = 90∘