Answer:
C = 29
Step-by-step explanation:
using pythagoras theorem since the angle is a right angled triangle
it states that hypothenus²= opposite² + adjacent²
the hypothenus is always the longest side
opposite and adjacent are interwoven
hyp² = 20² +21²
hyp² = 400 + 441
hyp² = 841
hyp = √841 = 29
