Câu 1=2

Câu 2=0

tick cái nha

63x(64-62)+62x(62-64)

=63x2+62x2

=(63+62)x2

=125x2

=250

Vì \(\frac{1}{13}+\frac{1}{14}+\frac{1}{15}<\frac{1}{12}+\frac{1}{12}+\frac{1}{12}=\frac{3}{12}=\frac{1}{4}\)

\(\frac{1}{61}+\frac{1}{62}+...+\frac{1}{66}<\frac{1}{60}+\frac{1}{60}+...+\frac{1}{60}=\frac{6}{60}=\frac{1}{10}\)

=> A < \(\frac{1}{3}+\frac{1}{4}+\frac{1}{10}=\frac{41}{60}<\frac{45}{60}=\frac{3}{4}\)điều phải c/m

3.20

a) (-28) + (-35) – 92 + (-82)

= -28 – 35 – 92 – 82 

= - (28 + 35 + 92 + 82)

= - [(28 + 82) + (35 + 92)]

= - (110 + 127)

= - 237.

b) 15 – (-38) + (-55) – (+47)

= 15 + 38 – 55 – 47

= 53 – 55 – 47

= - (55 – 53) – 47

= - 2 – 47

= - (2 + 47)

= - 49

Bài 3.20:

a: =-28-35-92-82

=-110-127

=-237

b: =15+38-55-47

=-40-47+38

=-2-47

=-49

Bài 3.21:

a: =62-81-12+59-9=50+50-81=19

b: =39-13-62-39=-75

Có trong SGK ko bro?

a=-97

b=-100

c=-210

d=-200

e=100

\(-62.\left(27-64\right)-64.\left(62-27\right)\)

\(=\left(-67\right).27+62.64-\left(-64\right).62+64.27\)

\(=\left(-67\right).27+64.27+62.24+64.62\)

\(=27.\left(-67+64\right)+62.\left(24+64\right)\)

\(=27.\left(-3\right)+62.88\)

\(=-81+5456\)

\(=5375\)

\(\dfrac{62.63+75}{12+62.64}=\dfrac{62.63+63+12}{12+62.64}=\dfrac{62.64+12}{12+62.64}=1\)

\(\dfrac{62\times63+75}{12+62\times64}=\dfrac{62\times\left(64-1\right)+63+12}{12+62\times64}=\dfrac{62\times64-62+63+12}{12+62\times64}=\dfrac{62\times64+1+12}{12+62\times64}=1\)

\(a,64^5=\left[8^2\right]^5=8^{10}\)

Giữ nguyên \(11^{10}\)

Mà \(8< 11\)=> \(8^{10}< 11^{10}\)hay \(64^5< 11^{10}\)

\(b,81^7=\left[9^2\right]^7=9^{14}\)

Giữ nguyên \(7^{14}\)

Mà \(9>7\)=> \(9^{14}>7^{14}\)hay \(81^7>7^{14}\)

c, Vì \(244>80\)=> \(244^{11}>80^{11}\)

d, Tương tự

a) 64⁵ và 11¹⁰

Ta có : 64⁵ = (8²)⁵ = 8^2.5 = 8¹⁰

Vì 8¹⁰ < 11¹⁰ nên 64⁵ < 11¹⁰

b) 81⁷ và 7¹⁴

Ta có : 81⁷ = (9²)⁷ = 9^2.7 = 9¹⁴

Vì 9¹⁴ > 7¹⁴ nên 81⁷ > 7¹⁴

c) 244¹¹ và 80¹¹

Vì 244 > 80 và số mũ bằng nhau nên 244¹¹ > 80¹¹

=))