>))))))))))))))))))):)

157
(x²-y²)/xy : (x-y)/3y * 1/(x+y) = (x-y)(x+y)/xy * 3y/(x-y) * 1/(x+y) =
3(x+y)/x * 1/(x+y) = ³/ₓ.
158
a/(a²-c²) * (a+c)/2ac : 1/(a-c) = a/(a-c)(a+c) * (a+c)/2ac : 1/(a-c) = 
1/2c(a-c) : 1/(a-c) = 1/2c(a-c) * (a-c)/1 = 1/2c.
159
1/x + x/y - (x+y)/xy = y/xy + x²/xy - (x+y)/xy = (y+x²)/xy - (x+y)/xy = 
(y+x²-x-y)/xy = (х²-x)/xy = х(х-1)/ху = (х-1)/у.
160
(a-b)/a + a/b - (a²-b²)/ab = (ab-b²)/ab + a²/ab - (a²-b²)/ab =
(ab-b²-a²)/ab - (a²-b²)/ab = (ab-b²-a²-a²+b²)/ab = (ab-a²)/ab = a(b-a)/ab = 
(b-a)/b.