bài trước đó sai đấy.

A=\(3 \left(\right. \frac{3}{20.23} + \frac{3}{23.26} + \frac{3}{26.29} + . . . + \frac{3}{77.80} \left.\right)\)

A\(= 3 \left(\right. \frac{1}{20} - \frac{1}{23} + \frac{1}{23} - \frac{1}{26} + \frac{1}{26} - \frac{1}{29} + . . . + \frac{1}{77} - \frac{1}{80} \left.\right)\)

\(A = 3 \left(\right. \frac{1}{20} - \frac{1}{80} \left.\right)\)

A\(= 3 \left(\right. \frac{4}{80} - \frac{1}{80} \left.\right)\)

A\(= 3. \frac{3}{80}\)

A\(= \frac{9}{80}\)

\(\frac{9}{80} < 1\)

⇒A<1

bài trước đó sai đấy.

A=\(3 \left(\right. \frac{3}{20.23} + \frac{3}{23.26} + \frac{3}{26.29} + . . . + \frac{3}{77.80} \left.\right)\)

A\(= 3 \left(\right. \frac{1}{20} - \frac{1}{23} + \frac{1}{23} - \frac{1}{26} + \frac{1}{26} - \frac{1}{29} + . . . + \frac{1}{77} - \frac{1}{80} \left.\right)\)

\(A=3\left(\right.\frac{1}{20}-\frac{1}{80}\left.\right)\)

A\(= 3 \left(\right. \frac{4}{80} - \frac{1}{80} \left.\right)\)

A\(= 3. \frac{3}{80}\)

A\(= \frac{9}{80}\)

\(\frac{9}{80}<1\)

⇒A<1

A=3^2/20.23+3^2/23.26+...+3^2/77.80
\(3 A = 3^{2} . \left(\right. \frac{1}{20.23} + \frac{1}{23.26} + . . . + \frac{1}{77.80} \left.\right)\)
\(3 A = 9. \left(\right. \frac{1}{20} - \frac{1}{23} + \frac{1}{23} - \frac{1}{26} + . . . + \frac{1}{77} - \frac{1}{80} \left.\right)\)
\(3 A = 9 \left(\right. \frac{1}{20} - \frac{1}{80} \left.\right)\)
\(3 A = 9 \left(\right. \frac{4}{80} - \frac{1}{80} \left.\right)\)
\(3 A = 9. \frac{3}{80}\)
\(3 A = \frac{21}{80}\)
\(A = \frac{21}{80} : 3\)
\(A = \frac{21}{80} . \frac{1}{3}\)
\(A = \frac{7}{80}\)
\(\frac{7}{80}\) <1

⇒A<1

​A=3^2/20.23+3^2/23.26+...+3^2/77.80
\(3 A = 3^{2} . \left(\right. \frac{1}{20.23} + \frac{1}{23.26} + . . . + \frac{1}{77.80} \left.\right)\)
\(3 A = 9. \left(\right. \frac{1}{20} - \frac{1}{23} + \frac{1}{23} - \frac{1}{26} + . . . + \frac{1}{77} - \frac{1}{80} \left.\right)\)
\(3 A = 9 \left(\right. \frac{1}{20} - \frac{1}{80} \left.\right)\)
\(3 A = 9 \left(\right. \frac{4}{80} - \frac{1}{80} \left.\right)\)
\(3 A = 9. \frac{3}{80}\)
\(3 A = \frac{21}{80}\)
\(A = \frac{21}{80} : 3\)
\(A = \frac{21}{80} . \frac{1}{3}\)
\(A = \frac{7}{80}\)
\(\frac{7}{80}\) <1

⇒A<1

giúp gì

công thức: \(\frac{a}{b\times(b+a)}=\frac{1}{b}-\frac{1}{\left.(b+a\right)}\)

\(\frac{1}{2\times3}+\frac{1}{3\times4}+\cdots+\frac{1}{49\times50}\)

=\(\frac12-\frac13+\frac13-\frac14+\cdots+\frac{1}{49}-\frac{1}{50}\)

=\(\frac12-\frac{1}{50}\)

=\(\frac{24}{50}\)

số học sinh giỏi của lớp 6A là

40x\(\frac{1}{4}\) = 10(học sinh)

số học sinh khá của lớp 6A là

10x\(\frac{3}{2}\) = 15(học sinh)

số học sinh trung bình của lớp là

40 - 10 - 15 = 15(học sinh)

đáp số: 10 học sinh giỏi////15 học sinh khá///15 học sinh trung bình

A = 3.(32,1 - 6,32) + 7.32,1 + 3.0,32

A = 3.32,1 - 3.6,32 + 7.32,1 + 3.0,32

A = (3.32.1 + 7.32,1) - (3.6,32 - 3.0,32)

A = 32,1(3 + 7) - 3.(6,32 - 0,32)

A = 32,1.10 - 3.6

A = 321 - 18

A = 303

dung dịch potassium hydroxide (KOH)