a) xy - y√x + √x - 1
= y√x.(√x - 1) + (√x - 1)
= (√x - 1).(y√x + 1)
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b) √ax - √by + √bx - √ay
= (√ax - √ay) + (√bx - √by)
= √a. (√x - √y) + √b.(√x - √y)
= (√x - √y).(√a + √b)
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c) 12 - √x - x
= 12 + 3√x - 4√x - x
= 3(4 + √x) - √x(4 + √x)
= (4 + √x)(3 - √x)