Bạn thay x vào biểu thức rồi dùng máy tính bấm là ra kết quả nha
c: Ta có: \(C=\left(x-y\right)^2+2\cdot\left(x^2-y^2\right)+\left(x+y\right)^2\)
\(=\left(x-y+x+y\right)^2\)
\(=4x^2\)
\(=4\cdot\dfrac{9}{16}=\dfrac{9}{4}\)
b: Ta có: \(B=\left(2x+1\right)^2-\left(x-1\right)^2-3\cdot\left(x-2\right)\left(x+2\right)\)
\(=4x^2+4x+1-x^2+2x-1-3x^2+12\)
\(=6x+12\)
=13
a) \(\left(x+2\right)\left(2x-4\right)-\left(2x+1\right)^2=2\left(x^2-4\right)-\left(2x+1\right)^2=2x^2-8-4x^2-4x-1=-2x^2-4x-9=-2\left(-\dfrac{1}{5}\right)^2-4.\dfrac{-1}{5}-9=-\dfrac{207}{25}\)b) \(B=\left(2x+1\right)^2-\left(x-1\right)^2=4x^2+4x+1-x^2+2x-1=3x^2+6x=2.\left(\dfrac{1}{6}\right)^2+6.\dfrac{1}{6}=\dfrac{19}{18}\)c) \(C=\left(x-y\right)^2+2\left(x^2-y^2\right)+\left(x+y\right)^2=\left(x-y+x+y\right)^2=4x^2=4.\left(0,75\right)^2=\dfrac{9}{4}\)
a. \(A=\left(x+2\right)\left(2x-4\right)-\left(2x+1\right)^2+2x\left(x-3\right)\)
\(=2x^2-8-4x^2-4x-1+2x^2-6x\)
\(=-10x-9\)
Thay \(x=-\dfrac{1}{5}\) vào A, ta được
\(A=\dfrac{10}{5}-9=2-9=-7\)
