Разбить. 18xy на. 20xy-2xy
5х^2+20xy-2ху-8у^2=(5х2+20ху)+(-2ху-8у^2)=5x•(х+4у)-2у•(х+4у)=(x+4y)(5х-2у)
1) √3*(√12+√3)=√3*√12+√3*√3=
![\sqrt{36} + \sqrt{9}](https://tex.z-dn.net/?f=%5Csqrt%7B36%7D+%2B+%5Csqrt%7B9%7D+)
= 6+3=9
2) (√20-√5)*√5= √20*√5<span>-√5)*√5= </span>
![\sqrt{100} - \sqrt{25}](https://tex.z-dn.net/?f=+%5Csqrt%7B100%7D+-++%5Csqrt%7B25%7D+)
= 10-5=5
((5k-5) / (k²-1) - k / (k+1)) : (5-k) / (k+1) = ((5k-5) / (k-1)(k+1) - k / (k+1)) :
(5-k) / (k+1) = ((5k-5) / (k-1)(k+1) - (k²-k) / (k-1)(k+1)) : (5-k) / (k+1) =
(5k-5-k²+k) / (k-1)(k+1) : (5-k) / (k+1) = (6k-k²-5) / (k-1)(k+1) : (5-k) / (k+1) =
(6k-k²-5)(k+1) / (k-1)(k+1)(5-k) = (6k-k²-5) / (k-1)(5-k) = (6k-k²-5) /
(5k-k²-5+k) = (6k-k²-5) / (6k-k²-5) = 1.