Question

Which angle in the figure below measures 90 degrees? Explain how you know

Answer 1

Given that

$\angle\text{BKD}=70^o\text{ and }\angle\text{DKC}=20^o$

We know that

$\angle BKC=\angle BKD+\angle DKC$

$\text{ Substitute }\angle\text{BKD}=70^o\text{ and }\angle\text{DKC}=20^o,\text{ we get}$

$\angle BKC=70^o+20^o$

Adding 70 and 20, we get

$\angle BKC=90^o$

Hence the angle BKC is 90 degrees.