﹙1﹚4a+4b/5ab·15a2b/a-b
=4(a+b)/5ab*15a^2*b/(a-b)
=4(a+b)*3a/(a-b)
=12a(a+b)/(a-b)
﹙2﹚x²-4y²／x²+4x+4·x+2／3x²+6xy
=[(x-2y)*(x+2y)*(x+2)]/[(x+2)^2*3x*(x+2y)]
=(x-2y)/[(x+2)*3x]
﹙3﹚x²+1／x-6·x²-36／x³+x
=[(x^2+1)*(x-6)*(x+6)]/[(x-6)*x*(x^2+1)]
=(x+6)/x
﹙4﹚y²-x²／5x^2-4xy ÷ x+y／5x-4y
=[(y-x)(y+x)*(5x-4y)]/[x(5x-4y)*(x+y)]
=(y-x)/x