初中数学-多项式的因式分解1.2a²-二分之一b²2.-4(x+2y)²+9(2x-y)²3.已知x+2y=3,x-2y=-2,求x²-4y²的值4.已知4m+n=90,2m-3n=10,求(m+2n)²-(3m-n)²的值
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![初中数学-多项式的因式分解1.2a²-二分之一b²2.-4(x+2y)²+9(2x-y)²3.已知x+2y=3,x-2y=-2,求x²-4y²的值4.已知4m+n=90,2m-3n=10,求(m+2n)²-(3m-n)²的值](/uploads/image/z/1239743-47-3.jpg?t=%E5%88%9D%E4%B8%AD%E6%95%B0%E5%AD%A6-%E5%A4%9A%E9%A1%B9%E5%BC%8F%E7%9A%84%E5%9B%A0%E5%BC%8F%E5%88%86%E8%A7%A31.2a%26%23178%3B-%E4%BA%8C%E5%88%86%E4%B9%8B%E4%B8%80b%26%23178%3B2.-4%EF%BC%88x%2B2y%EF%BC%89%26%23178%3B%2B9%EF%BC%882x-y%EF%BC%89%26%23178%3B3.%E5%B7%B2%E7%9F%A5x%2B2y%3D3%2Cx-2y%3D-2%2C%E6%B1%82x%26%23178%3B-4y%26%23178%3B%E7%9A%84%E5%80%BC4.%E5%B7%B2%E7%9F%A54m%2Bn%3D90%2C2m-3n%3D10%2C%E6%B1%82%EF%BC%88m%2B2n%EF%BC%89%26%23178%3B-%EF%BC%883m-n%EF%BC%89%26%23178%3B%E7%9A%84%E5%80%BC)
初中数学-多项式的因式分解1.2a²-二分之一b²2.-4(x+2y)²+9(2x-y)²3.已知x+2y=3,x-2y=-2,求x²-4y²的值4.已知4m+n=90,2m-3n=10,求(m+2n)²-(3m-n)²的值
初中数学-多项式的因式分解
1.2a²-二分之一b²
2.-4(x+2y)²+9(2x-y)²
3.已知x+2y=3,x-2y=-2,求x²-4y²的值
4.已知4m+n=90,2m-3n=10,求(m+2n)²-(3m-n)²的值
初中数学-多项式的因式分解1.2a²-二分之一b²2.-4(x+2y)²+9(2x-y)²3.已知x+2y=3,x-2y=-2,求x²-4y²的值4.已知4m+n=90,2m-3n=10,求(m+2n)²-(3m-n)²的值
1、原式=1/4(4a²-b²)=1/4(2a+b)(2a-b)
2、原式=(3(2x-y))²-(2(x+2y))²
=(3(2x-y)+2(x+2y))(3(2x-y)-2(x+2y))
=(8x+y)(4x-7y)
3、x²-4y²=(x+2y)(x-2y)=3*(-2)=-6
4、(m+2n)²-(3m-n)²=((m+2n)+(3m-n))((m+2n)-(3m-n))
=-(4m+n)(2m-3n)
=- 90*10
=-900
1。提取公倍数2得2(a²-1/4b²)=2(a+1/2b)(a-1/2b)
2.交换位置 平方差公式可得(3(2x-y)+2(x+2y))(3(2x-y)-2(x+2y))=(8x+y)(4x-7y)
3.平方差公式可得所求式子可化为(x+2y)(x-2y)=-6
4.同第三题可得所求式子(4m+n)(-2m+3n)=-900
1.把常数开方,[(根号下2)a+b/(根号下2)]*[[(根号下2)a-b/(根号下2)]
2.[3(2x-y)+2(x+2y)]*[3(2x-y)-2(x+2y)]=(8x+y)(4x-7y)
3.x²-4y²=(x+2y)(x-2y)=-6
4.(m+2n)²-(3m-n)²=[(m+2n)+(3m-n)]*[(m+2n)-(3...
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1.把常数开方,[(根号下2)a+b/(根号下2)]*[[(根号下2)a-b/(根号下2)]
2.[3(2x-y)+2(x+2y)]*[3(2x-y)-2(x+2y)]=(8x+y)(4x-7y)
3.x²-4y²=(x+2y)(x-2y)=-6
4.(m+2n)²-(3m-n)²=[(m+2n)+(3m-n)]*[(m+2n)-(3m-n)]=(4m+n)(3n-2m)=90*(-10)=-900
3和4不因式分解直接解方程也可以做
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1)原式=2(a²-四分之一b²)=2(a+二分之一b)(a-二分之一b)
2)原式=[3﹙2x-y﹚]²-[2﹙x+2y﹚]²=[3﹙2x-y﹚+2﹙x+2y﹚][3﹙2x-y﹚-2﹙x+2y﹚]
=﹙6x-3y+2x+4y﹚﹙6x-3y-2x-4y﹚=﹙8x+y﹚﹙4x-7y﹚
3)原式=﹙x+2y﹚﹙x-2y﹚=3×2=6
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1)原式=2(a²-四分之一b²)=2(a+二分之一b)(a-二分之一b)
2)原式=[3﹙2x-y﹚]²-[2﹙x+2y﹚]²=[3﹙2x-y﹚+2﹙x+2y﹚][3﹙2x-y﹚-2﹙x+2y﹚]
=﹙6x-3y+2x+4y﹚﹙6x-3y-2x-4y﹚=﹙8x+y﹚﹙4x-7y﹚
3)原式=﹙x+2y﹚﹙x-2y﹚=3×2=6
4)由4m+n=90减2m-3n=10得:2m+4n=80∴m+2n=40
由4m+n=90加2m-3n=10得:6m-2n=100∴3m-n=50
原式=40²-50²=﹙40+50﹚﹙40-50﹚=-900
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