Question

tìm y bt

a/ 3y^3 = 75y

b/ ( 3y - 4 )^2 - 9 . ( y - 1 ) . ( y - 3 ) = 13

 

Answer 1

a: \(3y^3=75y\)

=>\(y^3=25y\)

=>\(y^3-25y=0\)

=>\(y\left(y^2-25\right)=0\)

=>\(y\left(y-5\right)\left(y+5\right)=0\)

=>\(\left[{}\begin{matrix}y=0\\y-5=0\\y+5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}y=0\\y=5\\y=-5\end{matrix}\right.\)

b: \(\left(3y-4\right)^2-9\left(y-1\right)\left(y-3\right)=13\)

=>\(9y^2-24y+16-9\left(y^2-4y+3\right)=13\)

=>\(9y^2-24y+16-9y^2+36y-27=13\)

=>12y-11=13

=>12y=11+13=24

=>\(y=\dfrac{24}{12}=2\)