+\(\dfrac{1}{3^{100}}\) với
So sánh A = 1 3 + 1 3 2 + 1 3 3 + . .. + 1 3 99 với 1 2
Tính nhanh:3/2+7/6+13/12+21/20+...+133/132
3/2+7/6+13/12+21/20+...+133/132
=1+ 1/2 + 1+ 1/6 + 1+ 1/12 + 1+ 1/20+......+ 1+ 1/132
=(1+ 1 + 1+.....+ 1) + ( 1/2+ 1/6+1/12+ 1/20+....+ 1/132)
= 11+ ( 1/1×2+ 1/2×3+1/3×4+1/4×5+.....+1/11×12)
=11+ ( 1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+......+1/11-1/12)
=11+(1-1/12)
= 11+11/12
=143/12
Tính nhanh:3/2+7/6+13/12+21/20+...+133/132
3/2+7/6+13/12+21/20+...+133/132 =1+ 1/2 + 1+ 1/6 + 1+ 1/12 + 1+ 1/20+......+ 1+ 1/132 =(1+ 1 + 1+.....+ 1) + ( 1/2+ 1/6+1/12+ 1/20+....+ 1/132) = 11+ ( 1/1×2+ 1/2×3+1/3×4+1/4×5+.....+1/11×12) =11+ ( 1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+......+1/11-1/12) =11+(1-1/12) = 11+11/12 =143/12
Cho A = 13 + 132 + 133 + 134 + 135 + 136. Chứng tỏ rằng A ⋮ 2
A = 13 + 132 + 133 + 134 + 135 + 136
A = (13 + 132) + ( 133 + 134) + (135 + 136)
A = 13 \(\times\) ( 1 + 13) + 133 \(\times\) ( 1 + 13) + 135 \(\times\) ( 1 + 13)
A = 13 \(\times\) 14 + 133 \(\times\) 14 + 135 \(\times\) 14
A = 14 \(\times\) ( 13 + 133 + 135) vì 14 ⋮ 2
⇒ A ⋮ 2 ( đpcm)
132×145+100 _______________ 145×133-15
132*145+100-145*133+15
=145(132-133)+115
=-145+115=-30<0
=>132*145+100<145*133-15
132 x 145 + 100 / 145 x 133 -45
dau / la dau gach ngang cua phan so
132 * 145 + 100 trên 145 * 133 - 45
\(\frac{132×145+100}{145×133-45}=1\)
tinh nhanh 132*145+100/145*133 - 45
tính
133*66-166*12*132*66
100-99+898-97+96.-......4-3+2
17.75+16.25+14.75+13.25+........4,25+2.75+1,75
a ) 133*66 - 166*12 *132*66
= 133*66 - 262944*66
= 66 * ( 133 - 262944)
Sai đề
a ) 133 x 66 - 166 x 12 x 132 x 66
= 133 x 66 - 262944 * 66
= 66 x ( 133 - 262944)
Sai đề
a ) 133 x 66 - 166 x 12 x 132 x 66
= 133 x 66 - 262944 * 66
= 66 x ( 133 - 262944)