Tính nhanh: A = 2006 × 2008 – 20072.
Tính nhanh:
A = 2006 × 2008 – 20072.
Ta có:
A = 2006 × 2008 – 20072
A = 2006 × 2008 – 2007 × 2007
A = 2006 × (2007 + 1) – 2007 × (2006 + 1)
A = 2006 × 2007 + 2006 – 2007 × 2006 + 2007
A = 2006 – 2007
A = –1