I need help I don’t understand this

Step-by-step explanation:

lets say "a" for the empty line,

for small triangle; y^2 = 2^2 + x^2

right triangle; we say a for empty line, a^2= 6^2 + x^2

and big triangle covering both triangles, 8^2 = y^2 + a^2

lets add left sides and right sides in each;

x^2 + 4 + x^2 + 36 + y^2 + a^2 = y^2 + a^2 + 64 and we can delete same things for both sides

y^2 and a^2 can be deleted and 4+36 - 64

2(x^2)=24

x^2= 12

and x will be √12

so, y^2 = x^2 + 2^2 which means y^2 = 12+4 y=16

true

explanation: