1,
A+(-2x²+3x-4)=3x²-5+4x
A=3x²-5+4x-(-2x²+3x-4)
=3x²-5+4x+2X²-3X+4
=5X²+X-1;
2,
A-B+3C=0
C=(B-A)/3
=[5mn-6m²-9n²-(3m²-2n²+mn)]/3
=[5mn-6m²-9n²-3m²+2n²-mn]/3
=(4mn-9m²-7n²)/3
3
個位數(shù)字+十位數(shù)字=X
個位數(shù)字-十位數(shù)字=3
兩式相減:2(十位數(shù)字)=X-3,十位數(shù)字=(X-3)/2;
兩式相加:2(個位數(shù)字)=X+3,個位數(shù)字=(X+3)/2;
含x的代數(shù)式表示這個兩位數(shù) :
10(X-3)/2+(X+3)/2
=(10X-30+X+3)/2
=(11X-27)/2