Question

 

a) Chứng minh rằng:

      - (-a + b + c) + ( b + c - 1) = (b - c + 6) - (7 - a + b) + c

b) Cho A = a + b - 5

          B = -b - c +1

          C = b - c - 4

          D = b - a

   Chứng minh rằng A + B = C - D.

Answer 1

a)

-(-a+b+c)+(b+c-1)=a-b-c+b+c-1=a-1

(b-c+6)-(7-a+b)+c=b-c+6-7+a-b+c=a-1

suy ra -(-a+b+c)+(b+c-1)=(b-c+6)-(7-a+b)+c

Answer 2

b)A+B=a+b-5-b-c+1=a-c-4

C-D=(b-c-4)-(b-a)=b-c-4-b+a=a-c-4

suy ra A+B=C-D