Which three lengths could be the lengths of the sides of a triangle?

a.21 cm, 7 cm, 6 cm

b.10 cm, 15 cm, 24 cm

c.12 cm, 5 cm, 17 cm

d.9 cm, 22 cm, 11 cm

News cameras take an overhead picture of a crowd at an outdoor event journalist then count the total number of people in the picture and use the sample of estimate the total number of people in the crowd this process is an example of

Ineed me i stuck and i don’t want to get it wrong

If 2(a^2+b^2)=(a+b)^2 then, > a+b=0, > ab=0, > a=b, > 2a=b