Explanation:
Given : A rectangle 4 x 8 , a semicircle
Diagonal intersecting semicircle
To Find :Area of red part
Solution:
Angle AC make AB α = ∠BAC
tan α = BC/AB = 4/8 = 1/2
=> α = 26.565°
∠ECA = ∠BAC = α
EC = EF = 4
=> ∠CEF = 180° - 2α
∠AED = 45° as AE is diagonal of Square of side 4
=> ∠AEF + 180° - 2α + 45° = 180°
=> ∠AEF = 2α - 45° = 8.13°
in Left side area between square and circle is split in 2 Equal parts
(1/2) area - area AFG = area of Red part
in Left side area between square and circle = 4² - (1/4)π4²
= 3.4336 sq unit
half = 1.7168 sq unit
Now find area AFG = area ΔAEF - sector EGF
area ΔAEF
AE = 4√2 , EF = 4 angle = 8.13°
area ΔAEF = (1/2) 4√2 * 4 sin 8.13° = 1.6 sq unit
area sector EGF = (8.13/360)π4² = 1.135 sq unit
area AFG = 1.6 - 1.135 = 0.465 sq unit
Area of Red part = 1.7168 - 0.465 sq unit
= 1.2518 sq unit
= 1.252 sq unit
= 1.25 sq unit.
Hope this helps!!