hitunglah panjang diameternya

[tex]l \: = \: \ \frac{1}{4 \: } \pi {d}^{2} \\ 157 \: = \: \frac{1}{2} \times \frac{1}{4} \times \frac{22}{7} { \times } {d}^{2} \\ {d}^{2} = 157 \times 2 \times 4 \times \frac{7}{22} \\ {d}^{2} = 400 \\ d \: \ = \sqrt{400} \\ d = 20 \: cm[/tex]