(у+50):14=4
у+50=4*14
у+50=56
у=56-50
у=6
3.5+5,1/7-2,1/14=3.5+5.2/14-2.1/14=3.1/2+3.1/14=6.8/14=6.4/7
5(2x-y)-3(3x-2y) = 10y-5y-9x+6y = x-y
5^(-12) / (5^-7)^2=5^(-12) / (5^2*5^14)=5^(-12) / 5^16=5^(-12-16)=5^-28
или (если 12с плюсом)
5^12/(5^2*5^14)=5^(12-16)=5^-4=1/5^4=1/625