a, 

\(\begin{array}{l}15,3 - 21,5 - 3.1,5\\ = 15,3 - 21,5 - 4,5\\ = 15,3 - \left( {21,5 + 4,5} \right)\\ = 15,3 - 26\\ =  - \left( {26 - 15,3} \right)\\ =  - 10,7\end{array}\)

b, 

\(\begin{array}{l}2.\left( {{4^2} - 2.4,1} \right) + 1,25:5\\ = 2.\left( {16 - 8,2} \right) + 0,25\\ = 2.7,8 + 0,25\\ = 15,6 + 0,25\\ = 15,85\end{array}\)

a, 15 , 3 − 21 , 5 − 3.1 , 5 = 15 , 3 − 21 , 5 − 4 , 5 = 15 , 3 − ( 21 , 5 + 4 , 5 ) = 15 , 3 − 26 = − ( 26 − 15 , 3 ) = − 10 , 7 b, 2. ( 4 2 − 2.4 , 1 ) + 1 , 25 : 5 = 2. ( 16 − 8 , 2 ) + 0 , 25 = 2.7 , 8 + 0 , 25 = 15 , 6 + 0 , 25 = 15 , 85

\(2.\left(4^2-2.4,1\right)+1,25:5\)

\(=2.\left(16-8,2\right)+1,25:5\)

\(=2.7,8+1,25:5\)

\(=15,6+0,25\)

\(=15,85\)

c: \(C=5\cdot4^3+2^4\cdot5+41\)

\(=5\cdot64+16\cdot5+41\)

\(=320+80+41\)

\(=441=21^2\)

:)?

giúp e với em cần gấp ạ

\(A=3^2\cdot4^3-3^2+333\)

\(=3^2\cdot63+333\)

\(=3^2\cdot\left(63+37\right)\)

\(=30^2\)

\(B=5\cdot3^2+4\cdot3^2=3^2\cdot9=9^2\)

1)(-3,8+3,8)+(-5,7)=0-5,7=-5,7

2)(-31,4-(-6,4)+18=-25+18=-7

3)(3,1-3,1)-(2,5+2,5)=0

4)=0

5)-3,3

d: Ta có: \(D=5^3+6^3+59\)

\(=125+216+59\)

\(=400=20^2\)

Ông ơi

thằng  trung anh ơiiiiiiiiiiiii

Bài 1 :

\(M=\dfrac{30-2^{20}}{2^{18}}=\dfrac{2.15-2^{20}}{2^{18}}=\dfrac{15}{2^{17}}-2^2=\dfrac{15}{2^{17}}-4< 0\left(\dfrac{15}{2^{17}}< 1\right)\)

\(N=\dfrac{3^5}{1^{2021}+2^3}=\dfrac{3^5}{9}=\dfrac{3^5}{3^2}=3^3=27\)

\(\Rightarrow M< N\)

Bài 3 :

a) \(t^2+5t-8\) khi \(t=2\)

\(=5^2+2.5-8\)

\(=25+10-8\)

\(=27\)

b) \(\left(a+b\right)^2-\left(b-a\right)^3+2021\left(1\right)\)

\(\left\{{}\begin{matrix}a=5\\b=a+1=6\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}a+b=11\\b-a=1\end{matrix}\right.\)

\(\left(1\right)=11^2-1^3+2021=121-1+2021=2141\)

c) \(x^3-3x^2y+3xy^2-y^3=\left(x-y\right)^3\left(1\right)\)

\(\left\{{}\begin{matrix}x=3\\y=2\end{matrix}\right.\) \(\Rightarrow x-y=1\)

\(\left(1\right)=1^3=1\)

Bài 2 :

a) \(...=2^3\left(19-14\right)+1=8.5+1=41\)

b) \(...=100-\left[60:\left(5^2-15\right)\right]=100-\left[60:10\right]=100-6=94\)

c) \(...=160:\left[17+\left(9.5-\left(14+2^3\right)\right)\right]=160:\left[17+\left(45-22\right)\right]=160:\left[17+23\right]=160:40=4\)

d) \(...=798+100\left[16-2\left(25-22\right)\right]=798+100\left[16-2.3\right]=798+100.10=798+1000=1798\)