#15
[tex]\\ \bull\tt\dashrightarrow A=\dfrac{1}{2}\pi r^2[/tex]
[tex]\\ \bull\tt\dashrightarrow \pi r^2=2A[/tex]
[tex]\\ \bull\tt\dashrightarrow \pi=\sqrt{\dfrac{2A}{r}}[/tex]
#17
[tex]\\ \bull\tt\dashrightarrow 4m-n=1[/tex]
[tex]\\ \bull\tt\dashrightarrow 4m-1=n[/tex]
