X-5y=2x/2-10y/2
x-5y=x²/x-5xy/x
x-5y=4xy³/4y³-20y^4/4y³
x-5y=(x³-25xy²)/(x²-25y²)-(5x²y-125y³)/(x²-25y²)
ctg 40=1.1918
tg140= ctg50=0.8391
ctg40*tg140=1.1918*0.8391=1.0000393
Y ' = (ctg x - 1) ' = - 1 / sin^2 x
1)
а)3(х-4)=-5(х+2)
3х-12=-5х-10
3х+5х=12-10
8х=2/:8
х=0,25
б)1-2(х-2)=х-(4х+5)
1-2х+4=х-4х-5
-2х-х+4х=-4-5-1
х=-10
в)х+3/16=1/4 /:16
х+3=4
х+3=4
х=4-3
х=1