北师大版七年级下册数学习题1.2的答案拜托各位大神
1个回答
1.计算： (1) (3k+7k)+(4k-3k+1) =3k+7k+4k-3k+1 =3k+4k+7k-3k+1 =7k+4k+1 (2) (3x+2xy-1/2x)-(2x-xy+x) =3x+2xy-1/2x-2x+xy-x =3x-2x+2xy+xy-1/2x-x =x-3/2x+3xy =x(x-3/2+3y) (3) (7a+2a+b)-(3a+2a-b) =4a+2a+b-3a-2a+b =4a+2b =2(2a+b) (4) (1/2xy+y+1)+(x-1/2xy-2y-1) =1/2xy+y+1+x-1/2xy-2y-1 =x+y-2y+1/2xy-1/2xy+1-1 =x-y =(x+y)(x-y) 2.求下列整式的值： (1) 3x-(2x+5x-1)-(3x+1) =3x-2x+5x-1-3x-1 =3x-2x+5x-3x-1-1 =x+2x-2 =10+2×10-2 =100+20-2 =118 (2) (xy-3/2x-1/2)-(xy-3/2x+1) =xy-3/2y-1/2-xy+3/2x-1 =xy-xy+3/2x-3/2y-1 =3/2x-3/2y-1 =3/2×10/3-3/2×8/3-1 =5-4-1 =0 (3) (4y-(x+y)+(x-4y) =4y-x-y+x-4y =4y-4y-x+x-y =-y =-18
