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a)
$\overline{a}-\overline{b}=\left(3\overline{\text{i}}-5\overline{\text{j}}\right)-\left(-2\overline{\text{i}}+7\overline{\text{j}}\right)$
$5\overline{\text{i}}-12\overline{\text{j}}$
$\left|\overline{a}-\overline{b}\right|\ voidaan\ laskea\ Pythagoraan\ lauseella$
$x^2=5^2+12^2$
$x^2=169\ \parallel\sqrt{ }$

$x=13\ \left(tai\ -13\right)$

b)
$2\overline{a}+\overline{b}=2\left(3\overline{\text{i}}-5\overline{\text{j}}\right)+\left(-2\overline{\text{i}}+7\overline{\text{j}}\right)$
$4\overline{\text{i}}-3\overline{\text{j}}$
$\left|2\overline{a}+\overline{b}\right|\ voidaan\ laskea\ Pythagoraan\ lauseella$
$x^2=4^2+3^2$
$x^2=25\ \parallel\sqrt{ }$
$x=5\ \left(tai\ -5\right)$