(1)
(-2)^100+(-2)^99
=2^100-2^99
=2*2^99-2^99
=2^99
(2)
2^(n+1)+2^n=24
2^n*2+2^n=24
2^n*3=24
2^n=8=2^3
n=3
(n+2)(n-2)
=5*1=5