(1)(2x^2+x)-[4x^2-(3^2-x)],其中x= -1又3分之2 (2)若a+b=5,a^3+b^3=50,求a^2+b^2的值 (3)已知a-2b+3c=7,4a+3b-2c=3,求代数式5a+12b-13c的值 (4)已知3x^2-x=1,求代数式6x^3+7x^2-5x+2011的值 (5)若x:y:z=3:4:7,且2x-y+z=18,求x+2y-z的值
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![(1)(2x^2+x)-[4x^2-(3^2-x)],其中x= -1又3分之2 (2)若a+b=5,a^3+b^3=50,求a^2+b^2的值 (3)已知a-2b+3c=7,4a+3b-2c=3,求代数式5a+12b-13c的值 (4)已知3x^2-x=1,求代数式6x^3+7x^2-5x+2011的值 (5)若x:y:z=3:4:7,且2x-y+z=18,求x+2y-z的值](/uploads/image/z/3933390-30-0.jpg?t=%281%29%282x%5E2%2Bx%29-%5B4x%5E2-%283%5E2-x%29%5D%2C%E5%85%B6%E4%B8%ADx%3D+-1%E5%8F%883%E5%88%86%E4%B9%8B2+%282%29%E8%8B%A5a%2Bb%3D5%2Ca%5E3%2Bb%5E3%3D50%2C%E6%B1%82a%5E2%2Bb%5E2%E7%9A%84%E5%80%BC+%283%29%E5%B7%B2%E7%9F%A5a-2b%2B3c%3D7%2C4a%2B3b-2c%3D3%2C%E6%B1%82%E4%BB%A3%E6%95%B0%E5%BC%8F5a%2B12b-13c%E7%9A%84%E5%80%BC+%284%29%E5%B7%B2%E7%9F%A53x%5E2-x%3D1%2C%E6%B1%82%E4%BB%A3%E6%95%B0%E5%BC%8F6x%5E3%2B7x%5E2-5x%2B2011%E7%9A%84%E5%80%BC+%285%29%E8%8B%A5x%3Ay%3Az%3D3%3A4%3A7%2C%E4%B8%942x-y%2Bz%3D18%2C%E6%B1%82x%2B2y-z%E7%9A%84%E5%80%BC)
(1)(2x^2+x)-[4x^2-(3^2-x)],其中x= -1又3分之2 (2)若a+b=5,a^3+b^3=50,求a^2+b^2的值 (3)已知a-2b+3c=7,4a+3b-2c=3,求代数式5a+12b-13c的值 (4)已知3x^2-x=1,求代数式6x^3+7x^2-5x+2011的值 (5)若x:y:z=3:4:7,且2x-y+z=18,求x+2y-z的值
(1)(2x^2+x)-[4x^2-(3^2-x)],其中x= -1又3分之2 (2)若a+b=5,a^3+b^3=50,求a^2+b^2的值 (3)已知a-2b+3c=7,4a+3b-2c=3,求代数式5a+12b-13c的值 (4)已知3x^2-x=1,求代数式6x^3+7x^2-5x+2011的值 (5)若x:y:z=3:4:7,且2x-y+z=18,求x+2y-z的值
(1)(2x^2+x)-[4x^2-(3^2-x)],其中x= -1又3分之2 (2)若a+b=5,a^3+b^3=50,求a^2+b^2的值 (3)已知a-2b+3c=7,4a+3b-2c=3,求代数式5a+12b-13c的值 (4)已知3x^2-x=1,求代数式6x^3+7x^2-5x+2011的值 (5)若x:y:z=3:4:7,且2x-y+z=18,求x+2y-z的值
(1)(2x^2+x)-[4x^2-(3^2-x)]=2x^2+x-4x^2+3^2-x=9-2x^2=9-50/9=31/9
(2)若a+b=5,a^3+b^3=50,求a^2+b^2的值
a^3+b^3=(a+b)(a^2-ab+b^2)=50=5(a^2+b^2-ab) , a^2+b^2=10+ab
2(a^2+b^2)=20+2ab -------(1)
(a+b)^2=a^2+b^2+2ab=25 , a^2+b^2=25-2ab-------(2)
(1)+(2)
a^2+b^2=45
(3)已知a-2b+3c=7,4a+3b-2c=3,
5a+12b-13c=(4a+3b-2c)+(a-2b+3c)+11b+12c=11b-14c+10=-25+10=-15
4a-8b+12c=28------(1)
4a+3b-2c=3---------(2)
(2)-(1)
11b-14c=-25
(4)已知3x^2-x=1,求代数式6x^3+7x^2-5x+2011的值
6x^3+7x^2-5x+2011=x(6x^2+7x-5)+2011=x[2(3x^2-x)+9x-5]+2011=9x^2-3x+2011
=2014
(5)若x:y:z=3:4:7,且2x-y+z=18,求x+2y-z的值
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