A=nx²+3mx+5,B=4x²-3x-y²且4A-2B的值与字母x无关求m,n的值?咋做
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![A=nx²+3mx+5,B=4x²-3x-y²且4A-2B的值与字母x无关求m,n的值?咋做](/uploads/image/z/995008-40-8.jpg?t=A%3Dnx%26%23178%3B%2B3mx%2B5%2CB%3D4x%26%23178%3B-3x-y%26%23178%3B%E4%B8%944A-2B%E7%9A%84%E5%80%BC%E4%B8%8E%E5%AD%97%E6%AF%8Dx%E6%97%A0%E5%85%B3%E6%B1%82m%2Cn%E7%9A%84%E5%80%BC%3F%E5%92%8B%E5%81%9A)
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A=nx²+3mx+5,B=4x²-3x-y²且4A-2B的值与字母x无关求m,n的值?咋做
A=nx²+3mx+5,B=4x²-3x-y²且4A-2B的值与字母x无关求m,n的值?咋做
A=nx²+3mx+5,B=4x²-3x-y²且4A-2B的值与字母x无关求m,n的值?咋做
4A-2B
=4(nx²+3mx+5)-2(4x²-3x-y²)
=4nx²+12mx+20-8x²+6x+2y²
=(4n-8)x²+(12m+6)x+20+2y²
因它的值与字母x无关,所以可得含x项的系数为0,于是有:
4n-8=0 解得:n=2
12m+6=0 解得:m=-1/2
4A-2B
=4(nx²+3mx+5)-2(4x²-3x-y²)
=4nx²+12mx+20-8x²+6x+2y²
=(4n-8)x²+(12m+6)x+2y²+20
与字母x无关,
则,4n-8=0,12m+6=0
所以,n=2,m=-1/2