Answer :
we know that
the area A of the circular cross section of the pipe is
A=pi*r²
D=20 cm------------- > r=D/2=20/2=10 cm
then
A=pi*10²=100*pi cm²
the answer is A=100*pi cm²
the area A of the circular cross section of the pipe is
A=pi*r²
D=20 cm------------- > r=D/2=20/2=10 cm
then
A=pi*10²=100*pi cm²
the answer is A=100*pi cm²