Toán Lớp 7: Cho A=5x^2-4+6x^3-7+8x B=4x+7x^2-6x+3 Tính A+B; A-B; B-A; 2A-B; 2A+B; 4A+B; 2A-3B Nhanh giúp mình với ạ^^

Question

Toán Lớp 7:  Cho A=5x^2-4+6x^3-7+8x  B=4x+7x^2-6x+3 Tính A+B; A-B; B-A; 2A-B; 2A+B; 4A+B; 2A-3B Nhanh giúp mình với ạ^^

maingoctruc · Answer

A + B = (5x&sup2; - 4 + 6x&sup3; - 7 + 8x) + (4x + 7x&sup2;  - 6x + 3)             = 5x&sup2; - 4 + 6x&sup3; - 7 + 8x + 4x + 7x&sup2;  - 6x + 3             = 6x&sup3; + (5x&sup2; + 7x&sup2;) + (8x + 4x - 6x) + (-4 - 7 + 3)             = 6x&sup3; + 12x&sup2; + 6x - 8   A - B = (5x&sup2; - 4 + 6x&sup3; - 7 + 8x) - (4x + 7x&sup2;  - 6x + 3)            = 5x&sup2; - 4 + 6x&sup3; - 7 + 8x - 4x - 7x&sup2;  + 6x - 3            = 6x&sup3; + (5x&sup2; - 7x&sup2;) + (8x - 4x + 6x) + (-4 - 7 - 3)            = 6x&sup3;  - 2x&sup2; + 10x - 14   B - A = - (A - B)            = - (6x&sup3;  - 2x&sup2; + 10x - 14)            = - 6x&sup3;  + 2x&sup2; - 10x + 14   2A - B = 2(5x&sup2; - 4 + 6x&sup3; - 7 + 8x) - (4x + 7x&sup2;  - 6x + 3)              = (10x&sup2; - 8 + 12x&sup3; - 14 + 16x) - 4x - 7x&sup2;  + 6x - 3              = 10x&sup2; - 8 + 12x&sup3; - 14 + 16x - 4x - 7x&sup2;  + 6x - 3              = 12x&sup3; + (10x&sup2; - 7x&sup2;) + (16x - 4x + 6x) + (-8 - 14 - 3)              = 12x&sup3;  + 3x&sup2; + 18x - 25   2A + B = 2(5x&sup2; - 4 + 6x&sup3; - 7 + 8x) + (4x + 7x&sup2;  - 6x + 3)               = (10x&sup2; - 8 + 12x&sup3; - 14 + 16x) + 4x + 7x&sup2;  - 6x + 3               = 10x&sup2; - 8 + 12x&sup3; - 14 + 16x + 4x + 7x&sup2;  - 6x + 3               = 12x&sup3; + (10x&sup2; + 7x&sup2;) + (16x + 4x - 6x) + (-8 - 14 + 3)               = 12x&sup3;  + 17x&sup2; + 14x - 19   4A + B = 4(5x&sup2; - 4 + 6x&sup3; - 7 + 8x) + (4x + 7x&sup2;  - 6x + 3)               = (20x&sup2; - 16 + 24x&sup3; - 28 + 32x) + 4x + 7x&sup2;  - 6x + 3               = 20x&sup2; - 16 + 24x&sup3; - 28 + 32x + 4x + 7x&sup2;  - 6x + 3               = 24x&sup3; + (20x&sup2; + 7x&sup2;) + (32x + 4x - 6x) + (-16 - 14 + 3)               = 24x&sup3;  + 27x&sup2; + 30x - 27   2A - 3B = 2(5x&sup2; - 4 + 6x&sup3; - 7 + 8x) - 3(4x + 7x&sup2;  - 6x + 3)                = (10x&sup2; - 8 + 12x&sup3; - 14 + 16x) - (12x + 21x&sup2;  - 18x + 9)                = 10x&sup2; - 8 + 12x&sup3; - 14 + 16x - 12x - 21x&sup2;  + 18x - 9                = 12x&sup3; + (10x&sup2; - 21x&sup2;) + (16x - 12x + 18x) + (-8 - 14 - 9)                = 12x&sup3;  - 11x&sup2; + 22x - 31