Đáp án:
\(k.K = {\left( {2x - 1} \right)^2}\)
Giải thích các bước giải:
\(\begin{array}{l}
a.A = 7xy\left( {y - 3{x^2} - 2xy} \right)\\
b.B = 4\left( {x + y} \right) - \left( {x + y} \right)\left( {x + y} \right)\\
= \left( {x + y} \right)\left( {4 - x - y} \right)\\
c.C = {x^2} - 5x + 4x - 20\\
= x\left( {x - 5} \right) + 4\left( {x - 5} \right)\\
= \left( {x - 5} \right)\left( {x + 4} \right)\\
d.D = 2{x^2} - 4x + 5x - 10\\
= 2x\left( {x - 2} \right) + 5\left( {x - 2} \right)\\
= \left( {x - 2} \right)\left( {2x + 5} \right)\\
e.E = {x^2} + 5x + x + 5\\
= x\left( {x + 5} \right) + \left( {x + 5} \right)\\
= \left( {x + 5} \right)\left( {x + 1} \right)\\
f.F = {x^2} - 4x + 7x - 28\\
= x\left( {x - 4} \right) + 7\left( {x - 4} \right)\\
= \left( {x - 4} \right)\left( {x + 7} \right)\\
g.G = \left( {2x - 3y} \right)\left( {2x + 3y} \right)\\
h.H = \left( {9x - 1} \right)\left( {9x + 1} \right)\\
i.I = {\left( {5x} \right)^3} + {2^3}\\
= \left( {5x + 2} \right)\left( {25{x^2} - 10x + 4} \right)\\
k.K = {\left( {2x - 1} \right)^2}
\end{array}\)
