K1

a)
$\tan39°=\frac{x}{3{,}5cm}$
$x=3{,}5\tan39°$
$x=2{,}834...cm\approx2{,}8cm$
b)
$c^2=a^2+b^2-2ab\cos135°$
$x^2=17{,}0^2+16{,}3^2-2\cdot17\cdot16{,}3\cdot\cos135$
$x^2=946.568...\ \parallel\sqrt{ }$

$x=30{,}766...cm\approx30{,}8cm$

c)
$a^2+b^2=c^2$
$3^2+x^2=6^2$
$36-9=x^2$
$25=x^2$
$x=5$