✔ 最佳答案
已知:
x^2 + y^2 - 6x + 2y + 10 = 0
求:
( 3x^2 - 2xy - y^2 ) / ( 5x^2 - 7xy + 2y^2 ) = ?
Sol:
x^2 + y^2 - 6x + 2y + 10 = 0
x^2 - 6x + 9 + y^2 + 2x + 1 = 0
( x - 3 )^2 + ( y + 1 )^2 = 0
x = 3, y = - 1
( because the square of any real number always ≧ 0 )
( 3x^2 - 2xy - y^2 ) / ( 5x^2 - 7xy + 2y^2 )
= [ 3 * 3^2 - 2 * 3 * ( - 1 ) - ( - 1 )^2 ] / [ 5 * 3^2 - 7 * 3 * ( - 1 ) + 2 * ( - 1 )^2 ]
= ( 27 + 6 - 1 ) / ( 45 + 21 + 2 )
= 32 / 68
= 8 / 17
Ans: 8 / 17