Skorzystamy ze wzoru skróconego mnożenia na kwadrat różnicy:

${\left(a-b\right)}^2=a^2-2ab+b^2$

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a)

${\left(5-b\right)}^2=5^2-2\cdot 5\cdot b+b^2=25-10b+b^2=b^2-10b+25$      

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b)

${\left(a-4\right)}^2=a^2-2a\cdot 4+4^2=a^2-8a+16$  

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c)

${\left(3a-2b\right)}^2={\left(3a\right)}^2-2\cdot 3a\cdot 2b+{\left(2b\right)}^2=9a^2-12ab+4b^2$  

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d)

${\left(7x-1\right)}^2={\left(7x\right)}^2-2\cdot 7x+1^2=49x^2-14x+1$  

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e)

${\left(2\sqrt{2}-5x\right)}^2={\left(2\sqrt{2}\right)}^2-2\cdot 2\sqrt{2}\cdot 5x+{\left(5x\right)}^2=25x^2-20\sqrt{2}x+8$  

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f)

${\left(\sqrt{2}x-\sqrt{8}y\right)}^2={\left(\sqrt{2}x\right)}^2-2\cdot \sqrt{2}x\cdot \sqrt{8}y+{\left(\sqrt{8}y\right)}^2=2x^2-2\sqrt{16}xy+8y^2=$  
$=2x^2-2\cdot 4xy+8y^2=2x^2-8xy+8y^2$