Ta có:
a)\(h\left(m\right)=\left(m+1\right)\left(m-2\right)+\left(m-1\right)\left(m+4\right)+3\)
\(\Leftrightarrow h\left(m\right)=m^2-m-2+m^2+3m-4+3\)
\(\Leftrightarrow h\left(m\right)=2m^2+2m-3\)
b)\(f\left(x\right)=\left(2x+1\right)\left(x+3\right)+\left(x+1\right)^2\left(x+2\right)+\left(x+5\right)\left(x+1\right)\)
\(\Leftrightarrow f\left(x\right)=2x^2+7x+3+x^3+2x^2+x+2x^2+4x+2\)
\(\Leftrightarrow f\left(x\right)=x^3+6x^2+12x+5\)
c)\(g\left(a\right)=\left(a+1\right)\left(2a-3\right)+\left(a-7\right)\left(a-3\right)\)
\(\Leftrightarrow g\left(a\right)=2a^2-a-3+a^2-10a+21\)
\(\Leftrightarrow g\left(a\right)=3a^2-11a+18\)
c: Ta có: g=(a+1)(2a-3)+(a-7)(a-3)
\(=2a^2-3a+2a-3+a^2-10a+21\)
\(=3a^2-11a+18\)
