A circle is centered at The tangent to the circle at is extended to Line segment intersects the circle at Find the area of the circle. Measures = OS = 3, SR = 4, RQ = 4, PQ = 8
Draw QS in the direction of S through to M where M is on the circle
Secant-Tangent Theorem
PQ^2 = RQ( RQ +RM)
8^2 = 4 ( 4 + RM)
64 / 4 = 4 + RM
16 = 4 + RM
RM = 16 - 4
RM = 12
SM = RM - SR = 12 - 4 = 8
Connect OR, OM = radius of the circle = r
Note that cos RSO = - cos MSO
By the Law of Cosines
r^2 = SR^2 + SO^2 - 2(SR * SO) (-cos MSO)
r^2 = SM^2 + SO^2 - 2(SM * SO) cos (MSO) simplify this system
r^2 = 4^2 + 3^2 +2 ( 4 * 3) cos (MSO) (1)
r^2 = 8^2 + 3^2 - 2(8*3) cos (MSO)
4^2 + 3^2 + 24 cos (MSO) = 8^2 + 3^2 - 48cos (MSO)
25 + 24cos (MSO) = 73 - 48 cos (MSO)
72 cos MSO = 48
cos MSO = 48/72 = 2/3 (2)
Sub (2) into (1)
r^2 = 4^2 + 3^2 + 2 (4 *3)(2/3)
r^2 = 25 + 16
r^2 = 41
Area of circle = pi * r^2 = 41 pi