;
2 × 5 × sin( π / 12 ) = 10 × sin ( π / 12 ) ;
π/12 = ( 180° ) / 12 = 15°.
But, sin ( π/12 )
= sin 15°
= sin ( 45° - 30°)
= sin 45°· cos 30° - cos 45°· sin 30°
= (1/√2)·(√3 /2 ) - (1/√2)·(1/2)
= ( √3 - 1 ) / (2√2) = [tex] \frac{( \sqrt{6}- \sqrt{2} )}{4} [/tex] ;
Finally, ( 2.5 ) × ( 2.4 - 1.4 ) = 2.5 cm ;
