\(a+b+c=3\)

\(\Leftrightarrow a^3+b^3+c^3=27-3\left(a+b\right)\left(b+c\right)\left(c+a\right)\)

\(\Leftrightarrow a^3+b^3+c^3=27-3\left(3-c\right)\left(3-a\right)\left(3-b\right)\)

\(\Leftrightarrow a^3+b^3+c^3=27-3\left[\left(9-3a-3c+ca\right)\left(3-b\right)\right]\)

\(\Leftrightarrow a^3+b^3+c^3=27-3\left(27-9b-9a+3ab-9c+3cb+3ca-abc\right)\)

....

PT

\(\Leftrightarrow20y^2-150=3x\left(2y-5\right)\)

\(\Leftrightarrow3x=\frac{20y^2-150}{2y-5}\)

De \(x\in Z\Rightarrow\frac{20y^2-150}{2y-5}\in Z\)

Dat \(M=\frac{20y^2-150}{2y-5}=5\left(2y+5\right)-\frac{25}{2y-5}\)

De \(3x=M=10y+25-\frac{25}{2y-5}\in Z\Rightarrow\frac{25}{2y-5}\in Z\Rightarrow2y-5\in\left\{-5;-1;1;5\right\}\)

Ta tim duoc

\(y_1=0;y_2=2;y_3=3;y_4=5\)

\(\Rightarrow x_1=x_3=30;x_2=70;x_4=70\)

khó quá hà bạn ơi

ĐK \(x\ne0\)

Chia cả 2 vế cho \(\frac{1}{x}\)ta được

\(\frac{3}{3x-4+\frac{1}{x}}+\frac{13}{3x+2+\frac{1}{x}}=6\)

Đặt \(3x+\frac{1}{x}=y\)

\(\Rightarrow\frac{3}{y-4}+\frac{13}{y+2}=6\)

\(\Leftrightarrow16y-46=6\left(y-4\right)\left(y+2\right)\)

Đến đây tự giải nhé (Phá ngoặc rồi ghép cặp lại)

\(\left(x^2+4x+6\right)\left(x^2+6x+6\right)-3x^2\left(1\right)\)

Đặt \(x^2+5x+6=t\)Thay vào (1) ta được:

\(\left(t-x\right)\left(t+x\right)-3x^2\)

\(=t^2-x^2-3x^2\)

\(=t^2-4x^2\)

\(=\left(t-2x\right)\left(t+2x\right)\)Thay \(t=x^2+5x+6\)ta được:

\(\left(x^2+5x+6-2x\right)\left(x^2+5x+6+2x\right)\)

\(=\left(x^2+3x+6\right)\left(x^2+7x+6\right)\)

\(=\left(x^2+3x+6\right)\left(x^2+x+6x+6\right)\)

\(=\left(x^2+3x+6\right)\left[x\left(x+1\right)+6\left(x+1\right)\right]\)

\(=\left(x^2+3x+6\right)\left(x+1\right)\left(x+6\right)\)

TXĐ: \(D=\left(-1;1\right)\)

\(B=\frac{2018x+2019\sqrt{1-x^2}+2020}{\sqrt{1-x^2}}\)

\(=\frac{2018x+2020}{\sqrt{1-x^2}}+2019\)

Đặt  \(A=\frac{2018x+2020}{\sqrt{1-x^2}}>0\)vì \(-1< x< 1\)

=> \(\sqrt{1-x^2}.A=2018x+2020\)

=> \(\left(1-x^2\right)A^2=2018^2x^2+2.2018.2020x+2020^2\)

<=> \(\left(2018^2+A^2\right)x^2+2.2018.2020x+2020^2-A^2=0\)

pt trên có nghiệm <=> \(\Delta\ge0\)<=> \(\left(2018.2020\right)^2-\left(2018^2+A^2\right).\left(2020^2-A^2\right)\ge0\)

<=> \(A^4-\left(2020^2-2018^2\right)A^2\ge0\)

<=> \(A^2-8076\ge0\)

<=> \(A\ge\sqrt{8076}\)

"=" xảy ra <=> \(x=-\frac{1009}{1010}\left(tm\right)\)

Vậy GTNN của B = \(\sqrt{8076}+2019\) đạt tại  \(x=-\frac{1009}{1010}\)

a.BH=9 HC=16 HA=12

b. 

tamg BDC đồng dạng EHC=>g CBD= g HEC

tan HEC=HC\EH=HC\2AH=25\2.12=25\24

=>HEC=46 độ 10=CBD

Mình viết nhầm bài là:

Rút gọn biểu thức:         \(A = {{12} \over√3+√2+√5}\)

Mn ơi giúp mình với. Please!!!!!!!!!!!!!!!!!!!!!!!!!!