áp dụng hệ thức viet ta có :
\(x_1+x_2=-5\)
\(x_1x_2=-36\)
a, đặt bt = A
\(\Rightarrow A< 0\)
\(A=x_1x_2\left(x_1-x_2\right)=-36\left(x_1-x_2\right)\)
\(\Leftrightarrow\frac{A}{-36}=x_1-x_2\)
\(\Leftrightarrow\left(\frac{A}{-36}\right)^2=\left(x_1-x_2\right)^2\)( do 2 vế đều dương)
\(=\left(x_1+x_2\right)^2-4x_1x_2=\left(-5\right)^2-4\left(-36\right)=169\)
\(\Leftrightarrow\frac{A}{-36}=\sqrt{169}=13\)
\(\Leftrightarrow A=-468\)
b, đặt bt = B
\(B+4=2+\frac{2x_1+1}{x_2+2}+2+\frac{2x_2+1}{x_1+2}=\frac{2\left(x_1+x_2\right)+5}{x_2+2}+\frac{2\left(x_1+x_2\right)+5}{x_1+2}\)
\(=\left(2\left(x_1+x_2\right)+5\right)\left(\frac{1}{x_1+2}+\frac{1}{x_2+2}\right)\)
\(=\left(-2.5+5\right)\frac{x_1+x_2+4}{\left(x_1+2\right)\left(x_2+2\right)}=\left(-5\right).\frac{-5+4}{x_1x_2+2\left(x_1+x_2\right)+4}=\frac{5}{-36-2.5+4}=-\frac{5}{42}\)
\(\Leftrightarrow B=-\frac{173}{42}\)
mk làm hơi tắt 1 chút nếu không hiểu thì hỏi lại nha
