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Let's break this up:
Radius: 19
Diameter: 38
Circumference: 119.4
So...
The area of a circle with radius 19 is 1134
A = πr2 = π(d
2
)2 A = C2
4π
π = 3.1415
A = area
C = circumference or perimeter
r = radius, d = diameter
SOLUTION STEPS:
Area of a circle in terms of radius:
Area = π·r2 = 3.14·192 = 1134 square cm(*)
Area of a circle in terms of diameter:
Area = π·(d
2
)2 = 3.14·(38
2
)2 = 3.14·(19)2 = 1134 square cm(*)
Area of a circle in terms of circumference:
Area = C2
4π
= 119.42
4π
= 14256.36
(4·3.14)
= 14256.36
12.56
= 1134 square cm(*)
(*) 1134.1149479459 cm, exactly or limited to the precision of this calculator (13 decimal places).
Note: for simplicity, the operations above were rounded to 2 decimal places and π was rounded to 3.14.
Result in other units of area:
A circle of radius = 19 or diameter = 38 or circumference = 119.4 cm has an area of:
1.134 × 10-7 square kilometers (km²)
0.1134 square meters (m²)
1134 square centimeters (cm²)
1.134 × 105 square millimeters (mm²)
4.3784 × 10-8 square miles (mi²)
0.135625 square yards (yd²)
1.22063 square feet (ft²)
175.77 square inches (in²)