7) y2 - 2.y.7 + 72
= (y - 7)2
8) a2b2 - 2ab + 1
= (ab)2 - 2.ab.1 + 12
=(ab - 1)2
9) \(\dfrac{1}{4}-x+x^2\)
= \(\left(\dfrac{1}{2}\right)^2-2.\dfrac{1}{2}.x+x^2\)
= \(\left(\dfrac{1}{2}-x\right)^2\)
10) 36x2 + 60xy + 25y2
= (6x)2 + 2.6x.5y + (5y)2
= (6x + 5y)2
11) x2 - y2
=(x - y)(x + y)
12) 252 - x2
= (25 - x)(25 + x)
13) 25x2 - 9y2
= (5x)2 - (3y)2
= (5x - 3y)(5x + 3y)
14) 100x2 - 1
= (10x)2 - 12
= (10x - 1)(10x + 1)
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