\(A\) \(=\) \(3^2\) \(+\) \(6^2\) \(+\) \(9^2\) \(+\) \(...\) \(+\) \(30^2\)

\(A\) \(=\) \(3^2\).( \(1^2\) \(+\) \(2^2\) \(+\) \(3^2\) \(+\) \(...\) \(+\) \(10^2\))

\(A\) \(=\) \(9\) . \(385\)

\(A\) \(=\) \(3465\)

giải 

tổng số tiền của 3 quyên sách là:

\(120\) . \(3\) \(=\) \(360\) ( số tiền)

khi giảm giá còn lại số tiền là :

\(360\) \(:\) \(100\%\) \(.\) \(90\%\) \(=\) \(324\) (số tiền0

bạn lan dược trả số tiền là

\(350\) \(-\) \(324\) \(=\) \(26\) (số tiền)

a)\(x\) \(-\)  \(\dfrac{2}{3}\) \(=\) \(\dfrac{1}{6}\)

\(x\)        \(=\)\(\dfrac{1}{6}\)  \(+\) \(\dfrac{2}{3}\)

\(x\)        \(=\)\(\dfrac{5}{6}\)

b)2\(x\)  \(+\) \(\dfrac{1}{2}\)  \(=\) \(\dfrac{-5}{3}\)

2\(x\)      \(=\) \(\dfrac{-5}{3}\) \(-\)  \(\dfrac{1}{2}\)

2\(x\)      \(=\) \(\dfrac{-13}{6}\)

\(x\)        \(=\) \(\dfrac{-13}{6}\) \(:\) 2

\(x\)         \(=\)\(\dfrac{-13}{12}\)

c)3\(x\) \(+\)  \(\dfrac{3}{2}\) \(=\) \(x\) \(-\) \(\dfrac{5}{3}\)

3\(x\) \(-\) \(x\) \(+\) \(\dfrac{3}{2}\) \(=\) \(x\) \(-\) \(x\) \(-\) \(\dfrac{5}{3}\)

2\(x\) \(+\) \(\dfrac{3}{2}\) \(=\\ \) \(\dfrac{-5}{3}\) 

2\(x\) \(=\) \(\dfrac{-5}{3}\) \(-\) \(\dfrac{3}{2}\)

2\(x\) \(=\) \(\dfrac{-19}{6}\)

\(x\)  \(=\) \(\dfrac{-19}{6}\) \(:\) 2

\(x\)  \(=\) \(\dfrac{-19}{12}\)

a)\(\dfrac{11}{24}\)  \(-\) \(\dfrac{5}{41}\) \(+\)  \(\dfrac{13}{24}\)  \(+\) 0,5  \(-\) \(\dfrac{36}{41}\)

\(=\)0,5 \(-\)  ((\(\dfrac{11}{24}\)  \(+\)  \(\dfrac{13}{24}\)) \(-\)  (\(\dfrac{36}{41}\)  \(+\) \(\dfrac{5}{41}\)))

\(=\)\(\dfrac{1}{2}\)  \(-\) (1  \(-\) 1)

\(=\)\(\dfrac{1}{2}\)

b)\(\dfrac{1}{2}\).\(\dfrac{3}{4}\)\(+\)\(\dfrac{1}{2}\).\(\dfrac{1}{4}\)  \(+\) \(\dfrac{1}{2}\)

\(=\)\(\dfrac{1}{2}\).(\(\dfrac{3}{4}\)  \(+\) \(\dfrac{1}{4}\))  \(+\) \(\dfrac{1}{2}\)

\(=\)\(\dfrac{1}{2}\).1  \(+\) \(\dfrac{1}{2}\)

=1

c)(\(\dfrac{-3}{4}\))\(^2\):(\(\dfrac{-1}{4}\))\(^2\)+9.(\(\dfrac{-1}{9}\))+(\(\dfrac{-3}{2}\))

=\(\dfrac{9}{16}\):\(\dfrac{1}{8}\)+9.\(\dfrac{-29}{18}\)

=9+-1+(\(\dfrac{-3}{2}\))

=8+(\(\dfrac{-3}{2}\))

=\(\dfrac{13}{2}\)

d)\(\sqrt{0.25}\).(-3)\(^3\)-\(\sqrt{\dfrac{1}{81}}\):(\(\dfrac{-1}{3}\))\(^3\)

=\(\dfrac{1}{2}\).(-27)-\(\dfrac{1}{9}\):(\(\dfrac{-1}{27}\))

=

zzzz

zzzzz

a.2/3.5/4-

1.371742e+190 đấy :)