Bài 5:
Theo đề, ta có:
\(\left(2x+5\right)^2-4x^2-12x=41\)
\(\Leftrightarrow20x-12x=41+25=66\)
hay \(x=8.25\left(m\right)\)
Chu vi là:
\(\left[\left(2\cdot8.25+5\right)^2+\left(4\cdot8.25^2+12\cdot8.25\right)\right]\cdot2=1667\left(m\right)\)
Đúng 0
Bình luận (0)
Bài 3:
a: Ta có: \(A=\left(2a+3\right)^2-13\left(a+1\right)\left(a-1\right)+\left(3a-2\right)^2\)
\(=4a^2+12a+9+9a^2-12a+4-13\left(a^2-1\right)\)
\(=13a^2+13-13a^2+13\)
=26
b: Ta có: \(B=\left(4x-1\right)^3-\left(4x-3\right)\left(16x^2+3\right)\)
\(=64x^3-48x^2+12x-1-64x^3-12x+48x^2+9\)
=8
Đúng 0
Bình luận (0)
