3:
1: =-5bc*3a^3+4ab*5bc-5c^2*5bc
=-15a^3bc+20ab^2c-25bc^3
2: \(A=20a^3-12a^2b-20a^3-5a^2b\)
=-17a^2b
=-17*4*(-3)
=51*4=204
3: \(=x^3+x^2+x-x^3-x^2-x+5\)
=5
4: =>x^2-x-x^2+2x=5
=>x=5
5: =>x^3-x^2+x-x^3-x^2+m=-2x^2+x+5
=>m-2x^2+x=-2x^2+x+5
=>m=5
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