Question

giup mk bai nay voi  :

A = ( -2a +3b -4c ) - (-2a - 3b -4c ) 

a, Rut gon

b, tinh gia tri cua A khi a = 2012 ; b= -1 ; c= -2013

ai nhanh mk se cho 1 like

Answer 1

\(A=\left(-2a+3b-4c\right)-\left(-2a-3b-4c\right)\)

\(a,=-2a+3b-4c+2a+3b+4c\)

\(=\left(-2a+2a\right)+\left(3b+3b\right)+\left(-4c+4c\right)\)

\(=0+\left(3b+3b\right)+0\)

\(=3b+3b=2.3b\)

\(b,\)Thay \(a=2012;b=-1;c=-2013\)vào biểu thức \(A\) ta có \(:\)

     \(A=\left[-2.2012+3.\left(-1\right)-4.\left(-2013\right)\right]\)\(-\left[-2.\left(2012\right)-3.\left(-1\right)-4.\left(-2013\right)\right]\)

    \(A=0\)