已知4x-3y-6z=0,x+2y-7z=0,则x²+5y²+7z²分之2xy+2yz-6xz=?已知4x-3y-6z=0,x+2y-7z=0,则x的平方+5y的平方+7z的平方分之2xy+2yz-6xz=?
来源:学生作业帮助网 编辑:作业帮 时间:2024/08/17 08:27:18
![已知4x-3y-6z=0,x+2y-7z=0,则x²+5y²+7z²分之2xy+2yz-6xz=?已知4x-3y-6z=0,x+2y-7z=0,则x的平方+5y的平方+7z的平方分之2xy+2yz-6xz=?](/uploads/image/z/6855005-29-5.jpg?t=%E5%B7%B2%E7%9F%A54x-3y-6z%3D0%2Cx%2B2y-7z%3D0%2C%E5%88%99x%26sup2%3B%2B5y%26sup2%3B%2B7z%26sup2%3B%E5%88%86%E4%B9%8B2xy%2B2yz-6xz%3D%3F%E5%B7%B2%E7%9F%A54x-3y-6z%3D0%2Cx%2B2y-7z%3D0%EF%BC%8C%E5%88%99x%E7%9A%84%E5%B9%B3%E6%96%B9%2B5y%E7%9A%84%E5%B9%B3%E6%96%B9%2B7z%E7%9A%84%E5%B9%B3%E6%96%B9%E5%88%86%E4%B9%8B2xy%2B2yz-6xz%3D%EF%BC%9F)
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已知4x-3y-6z=0,x+2y-7z=0,则x²+5y²+7z²分之2xy+2yz-6xz=?已知4x-3y-6z=0,x+2y-7z=0,则x的平方+5y的平方+7z的平方分之2xy+2yz-6xz=?
已知4x-3y-6z=0,x+2y-7z=0,则x²+5y²+7z²分之2xy+2yz-6xz=?
已知4x-3y-6z=0,x+2y-7z=0,则x的平方+5y的平方+7z的平方分之2xy+2yz-6xz=?
已知4x-3y-6z=0,x+2y-7z=0,则x²+5y²+7z²分之2xy+2yz-6xz=?已知4x-3y-6z=0,x+2y-7z=0,则x的平方+5y的平方+7z的平方分之2xy+2yz-6xz=?
4x - 3y -6z = 0 .(1)式
x + 2y - 7z = 0 .(2)式
4 * (2)式 - (1)式
11y - 22z = 0 => y = 2z
带入(2)式得到 x = 7z - 2y = 3z
所以所求的式子
= ( (3z)² + 5 * (2z)² + 7z²) / ( 2* 3z * 2z + 2* 2z * z - 6* 3z *z)
= [(9 + 20 + 7)z²] / [(12 + 4 - 18) z²]
= 36 / -2
= -18