a)3x2-5x-2=3x2-6x+x-2
=3x(x-2)+(x-2)
=(3x+1)(x-2)
b)x2-7xy-10y2=x2-2xy-5xy-10y2
=x(x-2y)-5y(x-2y)
=(x-5y)(x-2y)
c)c) x2 +4xy-21y2=x2+7xy-3xy-21y2
=x(x+7y)-3y(x+7y)
=(x-3y)(x+7y)
d) 5x2 +6xy+y2=5x2+5xy+xy+y2
=5x(x+y)+y(x+y)
=(5x+y)(x+y)
e) x2 +2xy-15y2=x2+5xy-3xy-15y2
=x(x+5y)-3y(x+5y)
=(x-3y)(x+5y)
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