ab7 x 2 + 43 = 19ab

=> (100a + 10b + 7) x 2 + 43 = 1900 + 10a + b

=> 200a + 20b + 14 + 43 = 1900 + 10a + b

=> 190a + 19b = 1843

=> 19(10a + b) = 1843

=> ab = 97

các bạn giúp mình nhé

a, Vì OD vuông góc với OB => DOB = 90^o      

        OC vuông góc với OA => AOC = 90^o

Ta có: AOD + DOB = AOB

     => AOD + 90^o = AOB

     => AOD = AOB - 90^o

Lại có: BOC + AOC = AOB

      => BOC + 90^o = AOB

     => BOC = AOB - 90^o

=> AOD = BOC ( = 90^o )

b, Vì OM là tia p/g của COD

=> COM = MOD = DOC/2

Ta có: AOD + DOM = AOM

          BOC + COM = BOM

Mà AOD = BOC ; COM = MOD

=> AOM = BOM và OM nằm giữa OA, OB

=> OM là tia phân giác của AOB

Cam on ban

Tóan lớp 11 thì anh/chị nên sang ho c24.vn nhé!

\(a,-5x\left(x-3\right)\left(2x+4\right)-\left(x+3\right)\left(x-3\right)+\left(5x-2\right)\left(3x+4\right)\)

\(=-5x\left(2x^2-x-12\right)-\left(x^2-9\right)+15x^2+20x-6x-8\)

\(=-10x^3+5x^2+60x-x^2+9+15x^2+20x-6x-8\)

\(=-10x^3+19x^2+74x+1\)

\(b,\left(4x-1\right)x\left(3x+1\right)-5x^2.x\left(x-3\right)-\left(x-4\right)x\left(x-5\right)\)\(-7\left(x^3-2x^2+x-1\right)\)

\(=\left(4x^2-x\right)\left(3x+1\right)-5x^4-15x^3-\left(x^2-4x\right)\left(x-5\right)\)\(-7x^3+14x^2-7x+7\)

\(=12x^3+x^2-x-5x^4-15x^3-x^3+9x^2+20x\)\(-7x^3+14x^2-7x+7\)

\(=-5x^4-11x^3+24x^2+12x+7\)

\(c,\left(5x-7\right)\left(x-9\right)-\left(3-x\right)\left(2-5x\right)-2x\left(x-4\right)\)

\(=5x^2-52x+63-6+17x-5x^2-2x^2+8x\)

\(=-2x^2-27x+57\)

\(d,\left(5x-4\right)\left(x+5\right)-\left(x+1\right)\left(x^2-6\right)-5x+19\)

\(=5x^2+21x-20-x^3-x^2+6x+6-5x+19\)

\(=-x^3+4x^2+22x+5\)

\(e,\left(9x^2-5\right)\left(x-3\right)-3x^2\left(3x+9\right)-\left(x-5\right)\left(x+4\right)-9x^3\)

\(=9x^3-27x^2-5x+15-9x^3-27x^2-x^2+x+20-9x^3\)

\(=-9x^3-55x^2+4x+35\)

\(g,\left(x-1\right)^2-\left(x+2\right)^2\)

\(=x^2-2x+1-x^2-4x-4\)

\(=-6x-3\)

mk viết thiều nó bằng 0 nữa nhé 

bang 188336,44

Mk làm từng câu nhé !

a)\(A=\frac{x-\sqrt{x}}{x-1}\left(đk:x\ge0,x\ne1\right)\)

\(=\frac{\sqrt{x}\left(\sqrt{x}-1\right)}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\)(vì \(x\ge0\))

\(=\frac{\sqrt{x}}{\sqrt{x}+1}\)

\(B=\frac{x-4}{x+2\sqrt{x}}\left(đk:x>0,x\ne4\right)\)

\(=\frac{\left(\sqrt{x}-2\right)\left(\sqrt{x}+2\right)}{\sqrt{x}\left(\sqrt{x}-2\right)}=1+\frac{2}{\sqrt{x}}\)

a.\(DK:x\ge0,x\ne1\)

\(A=\frac{x-\sqrt{x}}{x-1}=\frac{\sqrt{x}\left(\sqrt{x}-1\right)}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}=\frac{\sqrt{x}}{\sqrt{x}+1}\)

\(DK:x\ge0\)

\(B=\frac{\left(\sqrt{x}+2\right)\left(\sqrt{x}-2\right)}{\sqrt{x}\left(\sqrt{x}+2\right)}=\frac{\sqrt{x}-2}{\sqrt{x}}\)

b.\(A-B=\frac{\sqrt{x}}{\sqrt{x}+1}-\frac{\sqrt{x}-2}{\sqrt{x}}=\frac{x-x+\sqrt{x}+2}{x+\sqrt{x}}=\frac{\sqrt{x}+2}{x+\sqrt{x}}>0\) 

\(\Rightarrow A-B>0\Rightarrow A>B\)

c.Ta co:\(A.B=\frac{\sqrt{x}}{\sqrt{x}+1}.\frac{\sqrt{x}-2}{\sqrt{x}}=\frac{\sqrt{x}-2}{\sqrt{x}+1}=1-\frac{3}{\sqrt{x}+1}\)

De \(A.B\in Z\)

\(\Rightarrow1-\frac{3}{\sqrt{x}+1}\in Z\)

\(\Rightarrow\frac{3}{\sqrt{x}+1}\in Z\)

\(\Rightarrow3⋮\sqrt{x}+1\)

\(\Rightarrow x=4\)

d.Ta co: \(A.B=\frac{\sqrt{x}-2}{\sqrt{x}+1}< \frac{1}{2}\)

\(\Leftrightarrow2\sqrt{x}-4< \sqrt{x}+1\)

\(\Leftrightarrow x< 25\)