# explain this question. What is this a1 a2 and all??

$a=2\hat{i}-\hat{j},b=2\hat{i}+\hat{j}\phantom{\rule{0ex}{0ex}}prjectionofaonb=\frac{a.b}{\left|b\right|}=\frac{4-1}{\sqrt{4+1}}=\frac{3}{\sqrt{5}}\phantom{\rule{0ex}{0ex}}solutioniswrongiftwovectorareperpendicularthena.b=0buta.b=3\phantom{\rule{0ex}{0ex}}Regards\phantom{\rule{0ex}{0ex}}$

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