Toán Lớp 8: a) 1/x-y+3xy/y^3-x^3+x-y/x^2+xy+y^2 b) 3/x^2+2xy+y^2+4/2xy-x^2-y^2+5/x^2-y^2

Question

Toán Lớp 8:  a)                1/x-y+3xy/y^3-x^3+x-y/x^2+xy+y^2 b)                 3/x^2+2xy+y^2+4/2xy-x^2-y^2+5/x^2-y^2

mocmien87 · Answer

Hướng dẫn trả lời:     a) {1}/{x - y} + {3xy}/{y^3 - x^3} + {x - y}/{x^2 + xy + y^2} (ĐKXĐ: x ne y)   = {1}/{x - y} - {3xy}/{x^3 - y^3} + {x - y}/{x^2 + xy + y^2}   = {1}/{x - y} - {3xy}/{(x - y)cdot(x^2 + xy + y^2)} + {x - y}/{x^2 + xy + y^2}   = {x^2 + xy + y^2}/{(x - y)cdot(x^2 + xy + y^2)} - {3xy}/{(x - y)cdot(x^2 + xy + y^2)} + {(x - y)^2}/{(x - y)cdot(x^2 + xy + y^2)}   = {(x^2 + xy + y^2) - 3xy + (x - y)^2}/{(x - y)cdot(x^2 + xy + y^2)}   = {x^2 + xy + y^2 - 3xy + x^2 - 2xy + y^2}/{(x - y)cdot(x^2 + xy + y^2)}   = {(x^2 + x^2) + (xy - 3xy - 2xy) + (y^2 + y^2)}/{(x - y)cdot(x^2 + xy + y^2)}   = {2x^2 - 4xy + 2y^2}/{(x - y)cdot(x^2 + xy + y^2)}   = {2cdot(x^2 - 2xy + y^2)}/{(x - y)cdot(x^2 + xy + y^2)}   = {2cdot(x - y)^2}/{(x - y)cdot(x^2 + xy + y^2)}   = {2cdot(x - y)}/{x^2 + xy + y^2}   b) {3}/{x^2 + 2xy + y^2} + {4}/{2xy - x^2 - y^2} + {5}/{x^2 - y^2} (ĐKXĐ: x ne y)   = {3}/{(x + y)^2} - {4}/{x^2 - 2xy + y^2} + {5}/{(x + y)cdot(x - y)}   = {3}/{(x + y)^2} - {4}/{(x - y)^2} + {5}/{(x + y)cdot(x - y)}   = {3cdot(x - y)^2}/{(x + y)^2cdot(x - y)^2} - {4cdot(x + y)^2}/{(x + y)^2cdot(x - y)^2} + {5cdot(x + y)cdot(x - y)}/{(x + y)^2cdot(x - y)^2}   = {3cdot(x^2 - 2xy + y^2) - 4cdot(x^2 + 2xy + y^2) + 5cdot(x^2 - y^2)}/{(x + y)^2cdot(x - y)^2}   = {3x^2 - 6xy + 3y^2 - 4x^2 - 8xy - 4y^2 + 5x^2 - 5y^2}/{(x + y)^2cdot(x - y)^2}   = {(3x^2 - 4x^2 + 5x^2) + (- 6xy - 8xy) + (3y^2 - 4y^2 - 5y^2)}/{(x + y)^2cdot(x - y)^2}   = {4x^2 - 14xy - 6y^2}/{(x + y)^2cdot(x - y)^2}   = {2cdot(2x^2 - 7xy - 3y^2)}/{(x + y)^2cdot(x - y)^2}