已知A=5x²-3y²+2xy,B=2x²+5y²-4xy,当x=1,y=-1时,求2A-5B的值
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![已知A=5x²-3y²+2xy,B=2x²+5y²-4xy,当x=1,y=-1时,求2A-5B的值](/uploads/image/z/8871014-38-4.jpg?t=%E5%B7%B2%E7%9F%A5A%3D5x%26%23178%3B-3y%26%23178%3B%2B2xy%2CB%3D2x%26%23178%3B%2B5y%26%23178%3B-4xy%2C%E5%BD%93x%3D1%2Cy%3D-1%E6%97%B6%2C%E6%B1%822A-5B%E7%9A%84%E5%80%BC)
已知A=5x²-3y²+2xy,B=2x²+5y²-4xy,当x=1,y=-1时,求2A-5B的值
已知A=5x²-3y²+2xy,B=2x²+5y²-4xy,当x=1,y=-1时,求2A-5B的值
已知A=5x²-3y²+2xy,B=2x²+5y²-4xy,当x=1,y=-1时,求2A-5B的值
2A-5B
=2(5x²-3y²+2xy)-5(2x²+5y²-4xy)
=10x²-6y²+4xy-10x²-25y²+20xy
=-31y²+24xy
当x=1,y=-1时
原式=-31-24=-55