в) P(x,y) = P1(x,y) + P2(x,y) – P3(x,y) = 27x3 – 27x2y + 9xy2 – y3 + + 20x3 – 15x2y + 4xy2 – 3y3 – 10x3 – 12x2y + 5xy2 – y2 = = 37x3 – 44x2y + 18xy2 – 4y3 – y2; г) P(x,y) = P1(x,y) – P2(x,y) – P3(x,y) = 27x3 – 27x2y + 9xy2 – y3 – – 20x3 + 15x2y – 4xy2 + 3y3 – 10x3 – 12x2y + 5xy2 – y2 = = – 3x3 – 24x2y + 10xy2 + 2y3 – y2. № 400 а) 2x2 – (2x2 – 5x) – (4x – 2) = 5; 2x2 – 2x2 + 5x – 4x + 2 = 5; x = 5 – 2; x = 3. Ответ: 3. б) 3y3 – (3y3 – 6y) – (3y + 4) = 2; 3y3 – 3y3 + 6y – 3y – 4 = 2; 3y = 6; y =2. Ответ: 2. в) (x2 – 7x – 11) – (5x2 – 13x – 18) = 16 – 4x2; x2 – 7x – 11 – 5x2 + 13x + 18 = 16 – 4x2; x2 – 5x2 + 4x2 – 7x + 13x = 16 – 18 +11; 6x = 9; x = 1,5. Ответ: 1,5. г) (y2 – 5y – 19) – (5y2 – 6y – 9) = 26 – 4y – 4y2; y2 – 5y – 19 – 5y2 + 6y + 9 = 26 – 4y – 4y2; y2 – 5y2 + 4y2 – 5y + 6y + 4y = 26 – 9 + 19; 5y = 36; y =7,2. Ответ: 7,2. № 401 Второй столбец 4x + 1 0 – 4mn – 2c2d – 3cd2 + 8
а) 9x + 7 – 5x – 6 = 4x + 1; б) a3 + 2a2b + b3 – a3 – 2a2b – b3 = 0; в) m2 – 2mn + n2 – m2 – 2mn – n2 = – 4mn; г) 0 – 2c2d – 3cd2 + 8 = – 2c2d – 3cd2 + 8.
№ 402 а) 6a2 – (2 – (1,56a – (a2 + 0,36a)) + (5,5a2 + 1,2a – 1)) = = 6a2 – (2 – 1,56a + a2 + 0,36a + 5,5a2 + 1,2a – 1) = = 6a2 – a2 – 5,5a2 + 1,56a – 0,36a – 1,2a – 2 + 1 = 0,5a2 – 1; б) (a2 + 2x2) – (5a2 – 1,2ax + (2,8x2 – (1,5a2 – 0,5ax + 1,8x2))) = = a2 + 2x2 – (5a2 – 1,2ax + (2,8x2 – 1,5a2 + 0,5ax – 1,8x2)) = = a2 + 2x2 – (5a2 – 1,2ax + 2,8x2 – 1,5a2 + 0,5ax – 1,8x2) = = a2 + 2x2 – 5a2 + 1,2ax – 2,8x2 + 1,5a2 – 0,5ax + 1,8x2 = = a2–5a2 +1,5a2 + 2x2 – 2,8x2 + 1,8x2 + 1,2ax – 0,5ax=– 2,5a2 + x2 + 0,7ax; в) 12,5x2 + y2 – (8x2 – 5y2 – ( – 10x2 + (5,5x2 – 6y2))) = = 12,5x2 + y2 – (8x2 – 5y2 – ( – 10x2 + 5,5x2 – 6y2)) = = 12,5x2 + y2 – (8x2 – 5y2 + 10x2 – 5,5x2 + 6y2) = = 12,5x2 + y2 – 8x2 + 5y2 – 10x2 + 5,5x2 – 6y2 = = 12,5x2 – 8x2 – 10x2 + 5,5x2 + y2 + 5y2 – 6y2 = 0;
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