Question

show that (1+z)^2=1+2z+z^2

Answer 1

(a+b)^2 = a^2+2ab+b^2
(1+z)^2 = 1^2 +2×1×z +z^2
(1+z)^2 = 1 +2z+z^2

Answer 2

Its a formula.

${(a + b)} ^{2} = {a}^{2} + {b}^{2} + 2ab$