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Lời giải:
$A=64^2-54^2=(64-54)(64+54)=10.118=1180$
$B=76^2+2.76.23+23^2=(76+23)^2=99^2=(100-1)^2=100^2-2.100+1$
$=10000-200+1=9801$
$C=88^2+62^2-38^2-12^2=(88^2-38^2)+(62^2-12^2)$
$=(88-38)(88+38)+(62-12)(62+12)$
$=50.126+50.74=50(126+74)=50.200=10000$
![](https://rs.olm.vn/images/avt/0.png?1311)
\(99^2=\left(100-1\right)^2=100^2-200+1=10000-200+1=9801\)
\(22^2=\left(20+2\right)^2=20^2+80+2^2=400+80+4=484\)
Câu cuối làm tương tự nhé
Chúc bạn học tốt!
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a) A=(2X^2+XY)+(4X+2Y)
=X(2X+Y) + 2(2X+Y)
= (2X+Y)(2+X)
Thay X=88,Y=-76
A=(2*88-76)(2+88)=100*90=9000
b) nhóm X^2 với -7X,XY với -7Y,làm tương tự thì B=6
![](https://rs.olm.vn/images/avt/0.png?1311)
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\(=\left(40^2-31^2\right)-\left(39^2-32^2\right)+\left(38^2-33^2\right)-\left(37^2-34^2\right)+\left(36^2-35^2\right)\)
\(=\left(40-31\right)\left(40+31\right)-\left(39-32\right)\left(39+32\right)+\left(38-33\right)\left(38+33\right)-\)
\(\left(37-34\right)\left(37+34\right)+\left(36-35\right)\left(36+35\right)\)
\(=9.71-7.71+5.71-3.71+1.71\)
\(=\left(9-7+5-3+1\right).71=5.71=355\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(40^2-39^2+38^2-37^2+....+32^2-31^2\)
\(=\left(40-39\right)\left(40+39\right)+\left(38-37\right)\left(38+37\right)+...+\left(32-31\right)\left(32+31\right)\)
\(=40+39+38+37+....+32+31\)
Số số hạng của dãy trên là: (40-31):1+1= 10 (số)
Tổng trên là: (40+31) x 10 : 2 = 355
Vậy ....
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fil in the correct form of the words in blackets( AS...........AS)
1. Jonh is ( tall)..........................Glen
2.Janet is ( beautiful) .............jenifer
3.You are (crazy ) .....................my sister
4.We are run(fast)...........they can
5.my mom is (not/strict)..........your mom
6. Your mobile phone is ( not/ expensve ) ........................mine
![](https://rs.olm.vn/images/avt/0.png?1311)
\(38^2+76\cdot12+12^2\)
\(=38^2+2\cdot38\cdot12+12^2\)
\(=\left(38+12\right)^2\)
\(=50^2\)
\(=2500\)
=1444+76x12+144
=1444+912+144
=2356+144
=2500
như này đúng ko
![](https://rs.olm.vn/images/avt/0.png?1311)
132^2 - 112^2 = (132 - 112) (132 + 112) = 20 . 244 = 4880
39 . 41 = (40 - 1) (40 + 1) = 402 - 1 = 1599
402 - 392 + 382 - 372 + ... + 22 - 1 = (402 - 392) + (382 - 372) + ... + (22 - 1)
= (40 - 39) (40 + 39) + (38 - 37) (38 + 37) + ... + (2 - 1) (2 + 1)
= 40 + 39 + 38 + 37 + 36 + ... + 2 + 1
= \(\frac{\left(40-1+1\right)\left(40+1\right)}{2}=\frac{40.41}{2}=820\)
`#3107.101107`
`38^2 + 76*12 + 12^2`
`= (38)^2 + 2*38*12 + (12)^2`
`= (38 + 12)^2`
`= 50^2`
`= 2500`
______
Sử dụng hđt:
`(A + B)^2 = A^2 + 2AB + B^2.`
\(38^2+76\cdot12+12^2\)
\(=38^2+2\cdot38\cdot12+12^2\)
\(=\left(38+12\right)^2=50^2=2500\)