Where the chord meets the circumference we can draw a radius to form an isosceles triangle where the equal sides are 5cm (radius). What is the angle at the centre? We can see the angle is 90 degrees, because the sum of the squares of the two sides 5^2+5^2=25+25=50 so the third side, which is the chord length, happens to be the square root of 50. The segment is therefore a quadrant, quarter the area of the circle, which has an area of (pi)r^2=25(pi). The area of the segment is 25(pi)/4=19.635sq cm approx.