show that (P+ⅈQ)^(1/n)+(P-ⅈQ)^(1/n)=2(P^2+Q^2 )^(1/2n)⋅cos⁡[1/n〖tan〗^(-1)⁡〖Q/P〗 ] and (x-1)^n=x^n

If n is a positive integer ,show that (P+ⅈQ)^(1/n)+(P-ⅈQ)^(1/n)=2(P^2+Q^2 )^(1/2n)⋅cos⁡[1/n 〖tan〗^(-1)⁡〖Q/P〗 ]
Solve (x-1)^n=(x)^n, n is a positive integer
these questions are taken from TS Telugu academy Intermediate second year mathematics 2A chapter DE MOIVRE'S Theorem exercise (b)