[tex]a) \ f(x) =2x^{2}+x(5\pi-x) = 2x^{2}+5\pi \cdot x + x\cdot(-x) = 2x^{2}+5\pi x -x^{2}=\boxed{x^{2}+5\pi x}[/tex]
[tex]b) \ (3x - 7)^{2} = (3x)^{2}-2\cdot3x\cdot7 + 7^{2} =\boxed{ 9x^{2}-42x+49}[/tex]
(a - b)² = a² - 2ab + b² - wzór skróconego mnożenia
[tex]c) \ f(x) = x^{2}-2(\sqrt{2}x^{2}+4) = x^{2}-2\sqrt{2}{x^{2}} -8 = \boxed{(1-\sqrt{2})x^{2}-8}[/tex]