1.以知m-2n=-2 ,求-3-2m+4n的值2.这样一道题、“已知A=2a²+2b²-3c²,B=3a²-b²-2c²,C=c²+2a²-3b²,当a=1,b=2,c=3时,求A-B+C的值”.有一个学生指出,题目中给出的b=2,c=3是多余的.他的
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![1.以知m-2n=-2 ,求-3-2m+4n的值2.这样一道题、“已知A=2a²+2b²-3c²,B=3a²-b²-2c²,C=c²+2a²-3b²,当a=1,b=2,c=3时,求A-B+C的值”.有一个学生指出,题目中给出的b=2,c=3是多余的.他的](/uploads/image/z/2467298-2-8.jpg?t=1.%E4%BB%A5%E7%9F%A5m-2n%3D-2+%2C%E6%B1%82-3-2m%2B4n%E7%9A%84%E5%80%BC2.%E8%BF%99%E6%A0%B7%E4%B8%80%E9%81%93%E9%A2%98%E3%80%81%E2%80%9C%E5%B7%B2%E7%9F%A5A%3D2a%26sup2%3B%2B2b%26sup2%3B-3c%26sup2%3B%2CB%3D3a%26sup2%3B-b%26sup2%3B-2c%26sup2%3B%2CC%3Dc%26sup2%3B%2B2a%26sup2%3B-3b%26sup2%3B%2C%E5%BD%93a%3D1%2Cb%3D2%2Cc%3D3%E6%97%B6%2C%E6%B1%82A-B%2BC%E7%9A%84%E5%80%BC%E2%80%9D.%E6%9C%89%E4%B8%80%E4%B8%AA%E5%AD%A6%E7%94%9F%E6%8C%87%E5%87%BA%2C%E9%A2%98%E7%9B%AE%E4%B8%AD%E7%BB%99%E5%87%BA%E7%9A%84b%3D2%2Cc%3D3%E6%98%AF%E5%A4%9A%E4%BD%99%E7%9A%84.%E4%BB%96%E7%9A%84)
1.以知m-2n=-2 ,求-3-2m+4n的值2.这样一道题、“已知A=2a²+2b²-3c²,B=3a²-b²-2c²,C=c²+2a²-3b²,当a=1,b=2,c=3时,求A-B+C的值”.有一个学生指出,题目中给出的b=2,c=3是多余的.他的
1.以知m-2n=-2 ,求-3-2m+4n的值
2.这样一道题、“已知A=2a²+2b²-3c²,B=3a²-b²-2c²,C=c²+2a²-3b²,当a=1,b=2,c=3时,求A-B+C的值”.有一个学生指出,题目中给出的b=2,c=3是多余的.他的说法有没有道理?为什么?
1.以知m-2n=-2 ,求-3-2m+4n的值2.这样一道题、“已知A=2a²+2b²-3c²,B=3a²-b²-2c²,C=c²+2a²-3b²,当a=1,b=2,c=3时,求A-B+C的值”.有一个学生指出,题目中给出的b=2,c=3是多余的.他的
解
1,-3-2m+4n=-3-(2m-4n)=-3+4=1
2,A-B+C=2a²+2b²-3c²-(3a²-b²-2c²)+c²+2a²-3b²
=2a²+2b²-3c²-3a²+b²+2c²+c²+2a²-3b²
=a²
所以不含b,c项,因此对
采纳哦
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