23/14 : (5/4 - 3/7) =2
1) 5/4 -3/7 = 35/28 -12/28 = 23/28
2) 23/14 : 23/28 = 23/14 * 28/23 = 2
1)0,027а¹²+b^9=(0,3а⁴)³+(b³)³=(0,3a⁴+b³)(0,09a⁸-0,3a⁴b³+b⁶)
2)20z²+3xy-15xz-4yz=(20z²-15xz)-(4yz-3xz)=5z(4z-3x)-y(4z-3x)=(4z-3x)(5z-y)
3)
N=S/2R...............n=S/2r