a: Xét ΔOAB và ΔOCD có

OA/OC=OB/OD

góc O chung

=>ΔOAB đồng dạng với ΔOCD

b: Xét ΔMDA và ΔMBC có

góc MAD=góc MCB

góc DMA=góc BMC

=>ΔMDA đồng dạng với ΔMBC

=>MD/MB=MA/MC

=>MD*MC=MB*MA

c: ΔOAB đồng dạng với ΔOCD

=>OA/OC=OB/OD=AB/CD=C OAB/ C OCD

=>C OAB/C OCD=OA/OC=8/6=4/3

=>C OAB/4=C OCD/3=38,5/7=5,5

=>C OAB=22; C OCD=16,5

=>AB+OA+OB=22 và CD+OC+OD=16,5

=>AB=22-8-4=10cm và CD=16,5-6-3=16,5-9=7,5cm

=>-3x^3yz^2-A=4x^3yz^2

=>A=-3x^3yz^2-4x^3yz^2=-7x^3yz^2

A = -7x³yz²

a: Xét ΔMBN và ΔMAE có

MN=ME

góc N=góc E

NB=EA

=>ΔMBN=ΔMAE

=>MA=MB

=>ΔMAB cân tại M

b: ΔNBM cân tại N

=>góc MBN=(180-45)/2=67,5 độ

ΔAMB cân tại M

=>góc AMB=180-2*67,5=45 độ

làm hộ mình đang cần gấp

=2(x-y)^4/2(x-y)^2+6(x-y)^5/2(x-y)^2+8(x-y)^7/2(x-y)^2

=(x-y)^2+3(x-y)^3+4(x-y)^5

\(F=\left(x^a+1\right)\left(x^a-2\right)-x^{a-2}\left(x^{a+2}-x^2\right)+2021\)

\(=x^{2a}-2x^a+x^a-2-x^{\left(a-2\right)+\left(a+2\right)}+x^{2+a-2}+2021\)

\(=x^{2a}-x^a-2-x^{2a}+x^a+2021\)

\(=\left(x^{2a}-x^{2a}\right)+\left(x^a-x^a\right)-2+2021\)

\(=2019\)

\(E=5x\left(x^2-7x+2\right)-x^2\left(5x-8\right)+27x^2-10x\)

\(=5x^3-35x^2+10x-5x^3+8x^2+27x^2-10x\)

\(=\left(5x^3-5x^3\right)+\left(-35x^2+8x^2+27x^2\right)+\left(10x-10x\right)\)

\(=0\)

\(D=\left(x^2-2\right)\left(x+2\right)-x^2\left(x+2\right)+2x\)

\(=x^3+2x^2-2x-4-x^3-2x^2+2x\)

\(=-4\)

\(C=\left(x+2\right)\left(x^2-2x+4\right)-x\left(x^2+5\right)-\left(8-5x\right)\)

\(=x^3-2x^2+4x+2x^2-4x+8-x^3-5x-8+5x\)

\(=0\)

\(B=2x\left(x+3\right)-\left(x-1\right)\left(8+2x\right)\)

\(=2x^2+6x-8x-2x^2+8+2x\)

\(=8\)

\(A=3x\left(x+5\right)-\left(3x+18\right)\left(x-1\right)\)

\(=3x^2+15x-3x^2+3x-18x+18\)

\(=18\)

cham vậy sao :"(

= x^3 - x^2 - x^2 + x + 5x - 5

= x^2(x-1) - x(x-1) + 5(x-1)

=(x^2 - x+ 5)(x-1)

\(x^3-2x^2+6x-5\)

\(=x^3-x^2+5x-x^2+x-5\) 

\(=x\left(x^2-x+5\right)-\left(x^2-x+5\right)\) 

\(=\left(x-1\right)\left(x^2-x+5\right)\) 

\(a,4+x^2+4x=0\)

\(\Leftrightarrow x^2+4x+4=0\)

\(\Leftrightarrow\left(x+2\right)^2=0\)

\(\Leftrightarrow x+2=0\)

\(\Leftrightarrow x=-2\)

Vậy \(S=\left\{-2\right\}\)

\(b,-6x+9+x^2=0\)

\(\Leftrightarrow x^2-6x+9=0\)

\(\Leftrightarrow\left(x-3\right)^2=0\)

\(\Leftrightarrow x-3=0\)

\(\Leftrightarrow x=3\)

Vậy \(S=\left\{3\right\}\)

thank you

\(x^2\left(x+y\right)-y\left(x^2-y^2\right)\)

\(=x^2\left(x+y\right)-y\left(x-y\right)\left(x+y\right)\)

\(=\left(x+y\right)\left[x^2-y\left(x-y\right)\right]\)

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

\(=x^3+y^3\)

Thay \(x=-6,y=8\) vào biểu thức đã rút gọn \(x^3+y^3\Rightarrow\left(-6\right)^3+8^3=296\)

\(87^2+73^2-27^2-13^2\)

\(=87^2-13^2+73^2-27^2\)

\(=\left(87^2-13^2\right)+\left(73^2-27^2\right)\)

\(=\left(87+13\right)\left(87-13\right)+\left(73+27\right)\left(73-27\right)\)

\(=74\cdot100+46\cdot100\)

\(=7400-4600\)

\(=2800\)

nói đi