( 1)(a^2+4ab-5b^2)/(a-b)

=(a-b)(a+5b)/(a-b)

=a+5b

(2)(a^2-5a+6)/(a^2-7a+ 12)

=(a-2)(a-3)/(a-3)(a-4)

=(a-2)/(a-4)

10.

∵x-2y=0,∴x=2y.

(x^2-3xy+y^2)/(2x^2+xy-3y^2)

=(4y^2-6y^2+y^2)/(8y^2+2y^2-3y^2)

=(4-6+ 1)/(8+2-3)

=- 1/7

1 1.

Original formula =a(a+b)/(a+b)(a-4b)

=a/(a-4b)

=0.5/(0.5-4*0.25)

=0.5/(-0.5)

=- 1

12.

Let x/2 = y/3 = z/4 = k.

Then x = 2k, y = 3k and z = 4k.

Original formula = (2k * 3k+3k * 4k+4k * 2k)/(4k2+9k2+16k2)

=26k^2/29k^2

=26/29