a: =16,71*(91+97)-188(6,2+0,67)

=16,71*188-188*(6,2+0,67)

=188(16,71-6,2-0,67)=1849,92

b: 56^2+31^2-13^2+56*62

=(56+31)^2-13^2

=87^2-13^2

=74*100=7400

a: \(2\cdot53\cdot12+4\cdot6\cdot87-3\cdot8\cdot40\)

\(=24\left(53+87-40\right)\)

=2400

b: \(5\cdot7\cdot77+7\cdot60+49\cdot25-45\cdot42\)

\(=35\cdot77+35\cdot12+49\cdot25-45\cdot42\)

\(=35\cdot89+35\left(7\cdot5-9\cdot6\right)\)

\(=35\cdot70=2450\)

a) 2.53.12+4.6.87-3.8.40

=24.53+24.87-24.40

=24.(53+87-40)

=24.100

=2400

b) 5.7.77-7.60+49.25-45.42

=5.7.77-7.60+7.7.25-45.6.7

=7.(5.77-60+7.25-6.45)

=7.230

=1610

`A=1/[1xx2xx3]+1/[2xx3xx4]+1/[3xx4xx5]+....+1/[98xx99xx100]`

`A=1/2xx(2/[1xx2xx3]+2/[2xx3xx4]+2/[3xx4xx5]+....+2/[98xx99xx100])`

`A=1/2xx(1/[1xx2]-1/[2xx3]+1/[2xx3]-1/[3xx4]+1/[3xx4]-1/[4xx5]+....+1/[98xx99]-1/[99xx100])`

`A=1/2xx(1/[1xx2]-1/[99xx100])`

`A=1/2xx(1/2-1/9900)`

`A=1/2xx(4950/9900-1/9900)`

`A=1/2xx4949/9900`

`A=4949/19800`

\(A=\dfrac{3-1}{1.2.3}+\dfrac{4-2}{2.3.4}+\dfrac{5-3}{3.4.5}+...+\dfrac{100-98}{98.99.100}\)

\(A=\left(\dfrac{1}{1.2}-\dfrac{1}{2.3}+\dfrac{1}{3.4}-\dfrac{1}{4.5}+...+\dfrac{1}{98.99}-\dfrac{1}{99.100}\right):2\)

\(A=\left(\dfrac{1}{2}-\dfrac{1}{6}+\dfrac{1}{12}-\dfrac{1}{20}+...+\dfrac{1}{9702}-\dfrac{1}{990}\right):2\)

\(A=\left(\dfrac{1}{2}-\dfrac{1}{990}\right):2\)

\(A=\dfrac{4949}{9900}:2\)

\(A=\dfrac{4949}{19800}\)

dốt toán : >>

a) \(29.31=\left(30-1\right)\left(30+1\right)=30^2-1=900-1=899\)

b) \(33,3^2-2.33,3.3,3+3,3^2=\left(33,3-3,3\right)^2=30^2=900\)

c) \(20,1.19,9=\left(20+0,1\right)\left(20-0,1\right)=20^2-0,1^2=400-0.01=399,99\)

d) \(37^2+2.37.13+13^2=\left(37+13\right)^2=50^2=2500\)

a, \(29.31=\left(30-1\right)\left(30+1\right)=30^2-1=899\)

b, \(33,3^2-2.33,3.3,3+3,3^2=\left(33,3-3,3\right)^2=30^2=900\)

c, \(20,1.19,9=\left(20-0,1\right)\left(20+0,1\right)=20^2-0,1^2=399,99\)

d, \(37^2+2.37.13+13^2=\left(37+13\right)^2=50^2=2500\)

a: \(29\cdot31=30^2-1=900-1=899\)

b: \(33.3^2-2\cdot33.3\cdot3.3+3.3^2\)

\(=\left(33.3-3.3\right)^2\)

=900

c: \(20.1\cdot19.9=20^2-0.1^2=399.9\)

d: \(37^2+2\cdot37\cdot13+13^2=\left(37+13\right)^2=2500\)

`@` `\text {Ans}`

`\downarrow`

Mình làm lại nhé ;-;

`@`` \text {Ans}`

`\downarrow`

Sửa lại đúng lớp đi c nhé.

đây ak  

\(c,=\left(2\sqrt{3}-6\sqrt{2}+5\sqrt{3}\right)\sqrt{3}+5\sqrt{6}\\ =\left(7\sqrt{3}-6\sqrt{2}\right)\sqrt{3}+5\sqrt{6}\\ =21-6\sqrt{6}+5\sqrt{6}=21-\sqrt{6}\\ f,=\sqrt{\dfrac{\left(\sqrt{3}-3\right)^2}{3-\sqrt{3}}}=\sqrt{\dfrac{\left(3-\sqrt{3}\right)^2}{3-\sqrt{3}}}=\sqrt{3-\sqrt{3}}\\ i,=\dfrac{7-4\sqrt{3}+7+4\sqrt{3}}{7^2-\left(4\sqrt{3}\right)^2}=\dfrac{14}{49-48}=\dfrac{14}{1}=14\)

\(e,=2\sqrt{3\cdot2}-2\sqrt{3}\cdot3+2^2-2\cdot2\cdot\sqrt{3}+\left(\sqrt{3}\right)^2+6\sqrt{3}\\ =2\sqrt{6}-6\sqrt{3}+4-4\sqrt{3}+3+6\sqrt{3}\\ =2\sqrt{6}-4\sqrt{3}+7\)

e,=2√3⋅2−2√3⋅3+22−2⋅2⋅√3+(√3)2+6√3=2√6−6√3+4−4√3+3+6√3=2√6−4√3+7

\(=2\sqrt{3.2}-3.2\sqrt{3}+2^2-2.2.\sqrt{3}+\left(\sqrt{3}\right)^2+6\sqrt{3}\)

\(=2\sqrt{6}-6\sqrt{3}+4-4\sqrt{3}+3+6\sqrt{3}\)

\(=2\sqrt{6}-4\sqrt{3}+7\)