Question

Cho:  a-4b=5 ; a.b=\(-\dfrac{3}{2}\)
a) A=16ab²-4a²b
b) B= a²+16b²
c) D= a+4b
 

Answer 1

\(\cdot a-4b=5\Leftrightarrow\left(a-4b\right)^2=a^2-8ab+16b^2=25\Leftrightarrow a^2+16b^2=25+8\cdot\left(-\dfrac{3}{2}\right)=13\\ \cdot a-4b=5\Leftrightarrow4b-a=-5\)

\(a,A=ab\left(4b-a\right)=-\dfrac{3}{2}\cdot\left(-5\right)=\dfrac{15}{2}\)

\(b,B=a^2+16b^2=13\left(cm.trên\right)\)

\(c,D=a+4b\)

Ta có \(\left(a+4b\right)^2=a^2+8ab+16b^2=13+8\cdot\left(-\dfrac{3}{2}\right)=1\)

\(\Rightarrow D=a+4b=1\)