1.你把(X+Y+Y)^3乘開,把值帶入就知道答案了
(X+Y+Z)^3 = X^3+Y^3+Z^3+6XYZ+3XY(X+Y)+3XZ(X+Z)+3YZ(Y+Z)
= X^3+Y^3+Z^3+6XYZ+3XY(7-Z)+3XZ(7-Y)+3YZ(7-X)
然後數字帶一帶...答案就出來了
至於第二題...嗯...拍勢...看不懂...