已知A=2xy-2y²+8x²,B=9x²+3xy-5y²(写不下了)(1)求-3A+2B (2)当x=1,y=-½时求-3A+2B的值
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![已知A=2xy-2y²+8x²,B=9x²+3xy-5y²(写不下了)(1)求-3A+2B (2)当x=1,y=-½时求-3A+2B的值](/uploads/image/z/3911426-26-6.jpg?t=%E5%B7%B2%E7%9F%A5A%3D2xy-2y%26%23178%3B%2B8x%26%23178%3B%2CB%3D9x%26%23178%3B%2B3xy-5y%26%23178%3B%EF%BC%88%E5%86%99%E4%B8%8D%E4%B8%8B%E4%BA%86%EF%BC%89%281%29%E6%B1%82-3A%2B2B+%282%29%E5%BD%93x%3D1%2Cy%3D%EF%BC%8D%26%23189%3B%E6%97%B6%E6%B1%82%EF%BC%8D3A%EF%BC%8B2B%E7%9A%84%E5%80%BC)
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已知A=2xy-2y²+8x²,B=9x²+3xy-5y²(写不下了)(1)求-3A+2B (2)当x=1,y=-½时求-3A+2B的值
已知A=2xy-2y²+8x²,B=9x²+3xy-5y²(写不下了)
(1)求-3A+2B (2)当x=1,y=-½时求-3A+2B的值
已知A=2xy-2y²+8x²,B=9x²+3xy-5y²(写不下了)(1)求-3A+2B (2)当x=1,y=-½时求-3A+2B的值
(1)-3A+2B
=-3(2xy-2y²+8x²)+2(9x²+3xy-5y²)
=-6xy+6y²-24x²+18x²+6xy-10y²
=-6x²-4y²
(2)当x=1, y=-½时,
-3A+2B
=-6x²-4y²
=-6×1²-4×(-½)²
=-6×1-4×¼
=-6-1
=-7
-3A+2B
=-3(2xy-2y²+8x²)+2(9x²+3xy-5y²)
=-6xy+6y²-24x²+18x²+6xy-10y²
=-6x²-4y²
x=1,y=-½时
-3A+2B
=-6x²-4y²
=-6x1²-4x(-1/2)²
=-6-4
=-10