\(12,25+\left(-21,37\right)-\left(14,67-21,75\right)\)

\(=12,25-21,37-14,67+21,75\)

\(=12,25+21,75-21,37-14,63-0,04\)

\(=34-36-0,04\)

= -2-0,04=-2,04

120:{54-[50:2.(3^2-2.4)]}

= 120:{ 54-[25.(9-8)]}

= 120:{54-[25.1]}

= 120:{54-25}

= 120:29

=\(\dfrac{120}{29}\)

\(\dfrac{1}{3}+\dfrac{1}{15}+\dfrac{1}{35}+...+\dfrac{1}{323}\\ =\dfrac{1}{2}\times\left(\dfrac{2}{1\times3}+\dfrac{2}{3\times5}+\dfrac{2}{5\times7}+...+\dfrac{2}{17\times19}\right)\\=\dfrac{1}{2}\times\left(\dfrac{1}{1}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{17}-\dfrac{1}{19}\right)\\ =\dfrac{1}{2}\times\left(\dfrac{1}{1}-\dfrac{1}{19}\right)\\ =\dfrac{1}{2}\times\dfrac{18}{19}=\dfrac{9}{19}\)

đề bài đây: 

\(\dfrac{1}{3}+\dfrac{1}{15}+\dfrac{1}{35}+...+\dfrac{1}{323}\)

43.11 = (10 + 10 + 10 + 10 + 3).11 = 110 + 110 + 110 + 110 + 33 = 440 + 33 = 473

67.99 = 67. (100 - 1) = 6 700 - 67 = 6 633

chắc làm theo cách này: )

=(8x125)x(50x2)x(45x10+45)
=1000x100x495
=49.500.000
 

= (8x125)x(50x2)x(45x10+45)
= 1000x100x495
= 49.500.000

g: \(\left(-3\right)^4\cdot10=81\cdot10=810\)

i: \(\left(-2\right)\cdot\left(-2\right)\cdot\left(-4\right)\cdot\left(-4\right)\cdot\left(-4\right)\)

\(=-2\cdot2\cdot4\cdot4\cdot4\)

\(=-2^2\cdot2^2\cdot2^2\cdot2^2=-2^8=-256\)

l: \(26\cdot\left(-125\right)-125\cdot\left(-36\right)\)

\(=125\cdot\left(-26\right)+125\cdot36\)

\(=125\left(-26+36\right)\)

\(=125\cdot10=1250\)

n: \(\left(-37\right)\cdot84+37\cdot\left(-16\right)\)

\(=37\cdot\left(-84\right)+37\cdot\left(-16\right)\)

\(=37\left(-84-16\right)=37\cdot\left(-100\right)=-3700\)

Sửa đề: \(45\cdot67+45\cdot34-45\)

\(=45\cdot\left(67+34-1\right)\)

\(=45\cdot100\)

\(=4500\)