luas lingkaran yang memiliki panjang diameter 40cm adalah....cm^2 a.phi 40 b.phi 80 c. phi 200 d. phi 400

Luas = π r²
         = phi (d/2)²
         = phi (40/2)²
         = phi (20)²
         = phi 400    ( D )

Luas:
[tex] = \pi.r {}^{2} \\ = \pi.( \frac{d}{2}) {}^{2} \\ = \pi.( \frac{40}{2} ) {}^{2} \\ = \pi.(20 {}^{} {}^{} ) {}^{2} \\ = \pi.400 \\ [/tex]
jadi, jawabanya D