a: \(f\left(-3\right)=2\cdot9+15+3=36\)
\(f\left(\dfrac{5}{2}\right)=2\cdot\dfrac{25}{4}-5\cdot\dfrac{5}{2}+3=3\)
\(f\left(\sqrt{2}\right)=2\cdot2-5\sqrt{2}+3=7-5\sqrt{2}\)
\(f\left(-1.5\right)=2\cdot2.25+5\cdot1.5+3=15\)
b: \(f\left(-3\right)=\left(-12-3\right)\left(9-6+2\right)=-15\cdot5=-75\)
\(f\left(\dfrac{5}{2}\right)=\left(10-3\right)\left(\dfrac{25}{4}+5+2\right)\)
\(=7\cdot\dfrac{53}{4}=\dfrac{371}{4}\)
\(f\left(\sqrt{2}\right)=\left(4\sqrt{2}-3\right)\left(2+2\sqrt{2}+2\right)\)
\(=\left(4\sqrt{2}-3\right)\left(2\sqrt{2}+4\right)\)
\(=16+16\sqrt{2}-6\sqrt{2}-12\)
\(=10\sqrt{2}+4\)