a)

n=int(input('nhap n: '))
a=[int(input('nhap a[%d]: '%i)) for i in range (n)]
kt=False
for i in range (n):
    if (a[i]<0):
        print(a[i],i)
        kt=True
        break
if (kt==False):
    print('khong co so am')

b)

n=int(input('nhap n: '))
a=[int(input('nhap a[%d]: '%i)) for i in range (n)]
kt=False
for i in range (n):
    if (a[i]>0):
        print(a[i],i)
        kt=True
        break
if (kt==False):
    print('khong co so duong')

$\color{red}{\text{#Daoanhviet96}}$

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Cách dùng index (mình làm câu a, câu b bạn tự làm):

n=int(input('nhap n: '))
a=[int(input('nhap a[%d]: '%i)) for i in range (n)]
s=[a[i] for i in range (n) if (a[i]<0)]
if (s==[]):
    print('khong co so am')
else:
    cs=a.index(s[0])
    print('gia tri:',a[cs])
    print('chi so:',cs)

a = [int(x) for x in input().split()]

find = False
for i in range(len(a)):
    if a[i] < 0:
        print(f'So am dau tien la {a[i]} o vi tri {i}')
        find = True
        break

if find == False:
    print('Khong tim thay so am')


find = False
for i in range(len(a)):
    if a[i] > 0:
        print(f'So duong dau tien la {a[i]} o vi tri {i}')
        find = True
        break

if find == False:
    print('Khong tim thay so duong')