数学初一M和N互为相反数,那磨（5M+2n)(2N+6M）=?请仔细讲解?已知M=2X+3RX2X+6,N=-2X+RX+2,且3M+6N的值与X无关,求R的值?一定要仔细讲解
2019-06-02
数学初一
M和N互为相反数,那磨（5M+2n)(2N+6M）=?请仔细讲解?已知M=2X+3RX_2X+6,N=-2X+RX+2,且3M+6N的值与X无关,求R的值?一定要仔细讲解
优质解答
1 因M与N为相反数,则M+N＝0
(5M+2N)(2N+6M)=(3M+2M+2N)(2N+2M+4M)=3M×4M=12M^2
2 3M+6N=3M+3N+3N=3(M+N)+3N=3N 代入N
3N=3×(-2X+RX+2)
=-6X+3RX+2
=(-6+3R)X+2
因其值与X无关,即该式中不含X项,即X项的系数为0,有
-6+3R＝0 → R=2
1 因M与N为相反数,则M+N＝0
(5M+2N)(2N+6M)=(3M+2M+2N)(2N+2M+4M)=3M×4M=12M^2
2 3M+6N=3M+3N+3N=3(M+N)+3N=3N 代入N
3N=3×(-2X+RX+2)
=-6X+3RX+2
=(-6+3R)X+2
因其值与X无关,即该式中不含X项,即X项的系数为0,有
-6+3R＝0 → R=2