標題:
一條未教過但係測試考既問題~~
發問:
x+y=5 而且xy=6 ,求x^2 ?y^2?? 我計到13,請問大家係咪呢? 真係識既朋友就請列出最詳細既步驟,plx!! 更新: 死火,多謝仁兄提醒,我真係當左加=.=咁就錯左題,岩岩仲諗緊自己會100分=.=
最佳解答:
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x2 ．y2 = (xy)2 = 62 = 36
其他解答:
x2 ．y2 = (xy)2 = 62 = 36|||||設 x = 2 和 y = 3 所以 x + y = 2 + 3 = 5 所以 xy = 2 x 3 = 6 x^2 x y^2 = xxyy = 2x2x3x3 =4x9 =36 簡單一D: xy= 6 (xy)^2= 6^2 x^2 ?y^2 = 36 明唔明, 唔明問我la...|||||有兩個做法 以下係較清楚既做法 x + y = 5 y = 5 - x --- 1 xy=6 --- 2 1代入2, x( 5 - x ) = 6 5x - x^2 = 6 x^2 -5x +6 = 0 (x - 3)(x - 2) = 0 x = 3 或 x = 2 當x = 3 , y = 5 - 3 = 2 x = 3, y = 2 x^2?y^2 = (3)^2 ?(2)^2 = 9?4 = 36 當x = 2, y = 5-2 = 3 x = 2, y = 3 x^2?y^2 = (2)^2 ?(3)^2 = 4?9 = 36 ∴x^2?y^2 = 36 以下係進階既做法 x^2?y^2 = (xy)^2 已知 xy = 6 ∴x^2?y^2 = (6)^2 = 36|||||x+y=5-----(1) xy=6-------(2) 從(1) x+y=5 x=5-y------(3) (3)加入(2) (5-y)y=6 5y-y^2=6 y^2-5y+6=0 (y-3)(y-2)=6 SO y=3 or y=2 x+3=5 or x+2=5 x=2 or x=3 x^2?y^2=3^2?2^2 =9?4 =36|||||x+y=5....(1) xy=6...(2) 係(1)啦...y=5-x...(3) 將(3)代入(2)啦wo... x(5-x)=6 -x^2+5x-6=0 x^2-5x+6=0 (x-2)(x-3)=0 x=2 or x =3 when x=2 y=3 when x=3 y=2 2^2x3^2 =4x9 =36 我想知你個 ?係加定乘??呢個應該係乘 = = 但係你個答案係加..|||||x+y=5 xy=6 So x or y一定=2同3 x=2 or x=3 / y=2 or y=3 都係一樣 2^2 ?3^2 =36
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