(2+4+...+16+18) x (45 x 3+ 5 x 45 - 90 x 4)
= A x (135 + 225 - 360)
= A x 0
= 0
Đáp án là : 0
Cách làm :
lấy 45 x 3 + 5 x 45 - 90 x 4
= 45 x 3 + 5 x 45 - 45 x 2 x 4
= 45 x 3 + 5 x 45 - 45 x 8
= 45 x (3 + 5 - 8)
= 45 x 0 = 45
giữ nguyên ( 2 + 4 + ...... + 16 + 18)
=(2 +4 + ... +16 +18) x (45 x 3 + 5 x 45 - 45 x 2 x 4 )
=(2 + 4+ ...+ 16 + 18) x (45 x [3 +5 - 2 x 4])
=(2 + 4 +...+ 16 +18) x (45 x [8 - 8])
=(2 + 4 + ...+ 16 + 18) x (45 x 0)
=(2 + 4 +... +16 +18)x0
= 0
=(2+4+...+18)x(45x3+5x45-45x2x4)
=90x(45x3+5x45-45x8)
=90x[45x(3+5-8)]
=90x[45x0]
=90x0
=0