Please check:

Question

1.Write in expanded form: this is a sigma notation-
4 on top
signma in middle
k=1 on bottom
to right of sigma is (k-1)(k-2)
I solved:
k=1 (1-1)(1-2)=0(-1)=0
K=2 (2-1)(2-2) = 1(0)=0
k=3(3-1)(3-2)=2(1)=2
k=4 (4-1)(4-)=3(2)=6
answer: 0+0+2+6

2. Write 4+9+16+25+36+49+64 in sigma notation
answer: 8 on top
sigma in middle
i=2 on bottom
x^2 to right of sigma
3. Write 88+79+70+61+...+-83 in sigma notation
my work:there is (-9) common difference
97-9(1)=88
97-9(2)=79
97-9(3)=70
97-9(4)=61
97-9(20)= -83
20 on top
sigma in middle
answer:i=1 on bottom to right of sigma is 97-9n

Answer 1

These look good to me except a typo in the first one
k=4 (4-1)(4-***2***)=3(2)=6

Answer 2

Thank you