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<br class="Apple-interchange-newline"><div></div>23+32+11+21+402
\(=8+9+1+2+1600\)
\(=\left(8+2\right)+\left(9+1\right)+1600\)
\(=10+10+1600\)
\(=20+1600\)
\(=1620\)
\(\frac{1}{1^2}+\frac{1}{2^2}+\frac{1}{3^2}+...+\frac{1}{50^2}\)
\(< 1+\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{49.50}\)
\(=1+\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{49}-\frac{1}{50}\)
\(=2-\frac{1}{50}< 2\)
Vế trái =VT
\(VT< 1+\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{49.50}\)
\(VT< 1+\frac{2-1}{1x2}+\frac{3-2}{2x3}+\frac{4-3}{3x4}+...+\frac{50-49}{49x50}\)
\(VT< 1+1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{49}-\frac{1}{50}=2-\frac{1}{50}< 2\)
\(\left(-2\right)+\left(-2\right)\)
\(=-4\)
\(22+\left(-2\right)\)
\(=20\)
\(22:2\)
\(=11\)
2+2*3+2+2+2+2+2+22+2+2+2+2+2+8
=2+6+2+2+2+2+2+22+2+2+2+2+10
=(6+22+2)+(2+2+2+2+2+2+2+2+2)+10
=30+18+10
48+10=58
=50+\(\infty\)
\(\infty\)=vo han