1.若代数式x^2+3x-5的值为2,则代数式2x^2+6x-3的值为____________.)2.(1)已知m^2-mn=21,mn-n^2=-12,求m^2-n^2与m^2-2mn+n^2的值.(2)已知x+2y+3z=10,4x+3y+2z=15,求x+y+z的值.3.已知当x=2时,ax^5+bx^3+cx+2的值为-3,求当x=-
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![1.若代数式x^2+3x-5的值为2,则代数式2x^2+6x-3的值为____________.)2.(1)已知m^2-mn=21,mn-n^2=-12,求m^2-n^2与m^2-2mn+n^2的值.(2)已知x+2y+3z=10,4x+3y+2z=15,求x+y+z的值.3.已知当x=2时,ax^5+bx^3+cx+2的值为-3,求当x=-](/uploads/image/z/2560359-39-9.jpg?t=1.%E8%8B%A5%E4%BB%A3%E6%95%B0%E5%BC%8Fx%5E2%2B3x-5%E7%9A%84%E5%80%BC%E4%B8%BA2%2C%E5%88%99%E4%BB%A3%E6%95%B0%E5%BC%8F2x%5E2%2B6x-3%E7%9A%84%E5%80%BC%E4%B8%BA____________.%EF%BC%892.%EF%BC%881%EF%BC%89%E5%B7%B2%E7%9F%A5m%5E2-mn%3D21%2Cmn-n%5E2%3D-12%2C%E6%B1%82m%5E2-n%5E2%E4%B8%8Em%5E2-2mn%2Bn%5E2%E7%9A%84%E5%80%BC.%EF%BC%882%EF%BC%89%E5%B7%B2%E7%9F%A5x%2B2y%2B3z%3D10%2C4x%2B3y%2B2z%3D15%2C%E6%B1%82x%2By%2Bz%E7%9A%84%E5%80%BC.3.%E5%B7%B2%E7%9F%A5%E5%BD%93x%3D2%E6%97%B6%2Cax%5E5%2Bbx%5E3%2Bcx%2B2%E7%9A%84%E5%80%BC%E4%B8%BA-3%2C%E6%B1%82%E5%BD%93x%3D-)
1.若代数式x^2+3x-5的值为2,则代数式2x^2+6x-3的值为____________.)2.(1)已知m^2-mn=21,mn-n^2=-12,求m^2-n^2与m^2-2mn+n^2的值.(2)已知x+2y+3z=10,4x+3y+2z=15,求x+y+z的值.3.已知当x=2时,ax^5+bx^3+cx+2的值为-3,求当x=-
1.若代数式x^2+3x-5的值为2,则代数式2x^2+6x-3的值为____________.)
2.(1)已知m^2-mn=21,mn-n^2=-12,求m^2-n^2与m^2-2mn+n^2的值.
(2)已知x+2y+3z=10,4x+3y+2z=15,求x+y+z的值.
3.已知当x=2时,ax^5+bx^3+cx+2的值为-3,求当x=-2时,ax^5+bx^3+cx+2的值.)
1.若代数式x^2+3x-5的值为2,则代数式2x^2+6x-3的值为____________.)2.(1)已知m^2-mn=21,mn-n^2=-12,求m^2-n^2与m^2-2mn+n^2的值.(2)已知x+2y+3z=10,4x+3y+2z=15,求x+y+z的值.3.已知当x=2时,ax^5+bx^3+cx+2的值为-3,求当x=-
第一题:
x^2+3x-5=2
x^2+3x=7
两边同乘以2,得到2x^2+6x=14,变换成 2x^2+6x-3=11.
第二题:
m^2-n^2=(m^2-mn)+(mn-n^2)=21+(-12)=9
m^2-2mn+n^2=(m^2-mn)-(mn-n^2)=21-(-12)=33
第三题:
因为x=2时,ax^5+bx^3+cx+2的值为-3,即ax^5+bx^3+cx=-5
而当x=-2时,ax^5+bx^3+cx这部分的值为x=2时的相反数,不知你能不能理解,因为系数不变,而x都是奇数次方,-1的奇数次方都是-1,将-1提出就能看出来.
所以当x=-2时,ax^5+bx^3+cx=+5,则此时ax^5+bx^3+cx+2=7
1:
x^2+3x-5=2
x^2+3x=7
两边同乘以2,得到2x^2+6x=14,变换成 2x^2+6x-3=11.
2:
m^2-n^2=(m^2-mn)+(mn-n^2)=21+(-12)=9
m^2-2mn+n^2=(m^2-mn)-(mn-n^2)=21-(-12)=33
3:
因为x=2时,ax^5+bx...
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1:
x^2+3x-5=2
x^2+3x=7
两边同乘以2,得到2x^2+6x=14,变换成 2x^2+6x-3=11.
2:
m^2-n^2=(m^2-mn)+(mn-n^2)=21+(-12)=9
m^2-2mn+n^2=(m^2-mn)-(mn-n^2)=21-(-12)=33
3:
因为x=2时,ax^5+bx^3+cx+2的值为-3,即ax^5+bx^3+cx=-5
而当x=-2时,ax^5+bx^3+cx这部分的值为x=2时的相反数,不知你能不能理解,因为系数不变,而x都是奇数次方,-1的奇数次方都是-1,将-1提出就能看出来。
所以当x=-2时,ax^5+bx^3+cx=+5,则此时ax^5+bx^3+cx+2=7
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