Đáp án:
Giải thích các bước giải:
P+Q=5xyz+2xy-3x²-11+(15-5x²+5xyz+2xy)
=5xyz+2xy-3x²-11+15-5x²+5xyz+2xy
=10xyz+4xy-8x²+4
P-Q=5xyz+2xy-3x²-11-(15-5x²+5xyz+2xy)
=5xyz+2xy-3x²-11-15+5xx²-5xyz-2xy
=2x²-26
3Q=3(15 - 5x² + 5xyz +2xy.)
⇔3Q=45-15x²+15xyz+6xy
⇒P-3Q=5xyz + 2xy - 3x² -11-(45-15x²+15xyz+6xy)
=5xyz + 2xy - 3x² -11-45+15x²-15xyz-6xy
=-10xyz-4xy+12x²-56