Question

如果分别以R,r为半径画同心圆(R》r),且得圆环的面积是10π,求代数式【4(R+r)方x(R

Answer 1

4(R+r)²x(R²-r²)

=4[(R+r)(R-r)]²

=4(R²-r²)²

=4[π（R²-r²)÷π]²

=4(10π÷π）²

=400

长见识了