1.) (√x - √y) (x + √xy + y)
=> x√x + x√y + √xy - x√y - y√x - y√y
=> x√x + √xy - y√x - y√y
2.) (√z + 2)(z - 2√z + 4)
=> z√z - 2z + 4√z + 2z - 4√z + 8
=> z√z + 8
3.) (5√t + 7)(25t - 35√t + 49)
=> 125t√t - 175t + 245√t + 175t - 245√t + 343
=> 125t√t + 343
4.) (√2 - √2s)(2 + 2√2s + 4s)
=> 2√2 + 4√s + 4s√2 - 2√2s - 4s - 4s√2s
=> 2√2 + 4(√s - s) + (4s√2)(1 - √s)
=> 2[√2 + 2(√s - s) + (2s√2)(1 - √s)]