Guys, My good you help.

L=1/4x3,14x10x10
  =1/4x314=78,5 cm²

if 1/4 circle
luas = 1/4*π*r²
= 1/4*3.14*10*10
= 1/4*314cm²
= 78.5cm²

if triangle
luas = 1/2*a*t
= 1/2*10*10
=5*10
=50cm²