-3x³y+27xy
= -3xy(x²-9)
= -3xy(x+3)(x-3)
2.
39*17-13*3^4
= 39*17 - 39*3^3
= 39*(17-27)
= -39*
5*3^4+24*3^3+63*3^2
= 15*3^3+24*3^3+21*3^3
= 3^3*(15+24+21)
= 27*60
= 1620
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