Będziemy korzystać ze wzorów skróconego mnożenia na kwadrat sumy i kwadrat różnicy.

Przypominamy je poniżej:

${\left(a+b\right)}^2=a^2+2ab+b^2$  

${\left(a-b\right)}^2=a^2-2ab+b^2$  

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$\text{a)}{12}^2={\left(10+2\right)}^2={10}^2+2\cdot 10\cdot 2+2^2=100+40+4=144$  

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$\text{b)}{21}^2={\left(20+1\right)}^2={20}^2+2\cdot 20\cdot 1+1^2=400+40+1=441$  

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$\text{c)}{19}^2={\left(20-1\right)}^2={20}^2-2\cdot 20\cdot 1+1^2=400-40+1=361$  

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$\text{d)}{18}^2={\left(20-2\right)}^2={20}^2-2\cdot 20\cdot 2+2^2=400-80+4=324$  

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$\text{e)}{32}^2={\left(30+2\right)}^2={30}^2+2\cdot 30\cdot 2+2^2=900+120+4=1024$  

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$\text{f)}{98}^2={\left(100-2\right)}^2={100}^2-2\cdot 100\cdot 2+2^2=10000-400+4=9604$  

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$\text{g)}{101}^2={\left(100+1\right)}^2={100}^2+2\cdot 100\cdot 1+1^2=10000+200+1=10201$  

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$\text{h)}{49}^2={\left(50-1\right)}^2={50}^2-2\cdot 50\cdot 1+1^2=2500-100+1=2401$