Question

关于初一合并同类项、求值的题1.2(X-3Y)² - 3(X-3Y)³ - (3Y-X)²

Answer 1

1.2(X-3Y)² - 3(X-3Y)³ - (3Y-X)²+(3Y-X)³.

=【2(3Y-X)²- (3Y-X)²】+【- 3(X-3Y)³-(X-3Y)³】

=(3Y-X)²-4(X-3Y)³

2.若使代数式2a²+3kab+b² - 6ab+9不含ab项,求k的值.

2a²+3kab+b² - 6ab+9

=2a²+（3K-6）ab+b²+9

∵原式中不含有ab项

∴ab项系数为0

3K-6=0

3K=6

K=2