81.

If , then x is equal to

• 
• 

• ab + bc + ca

• ab + bc + ca

Find the sum of:

• n

• 

• (n + 1)

• (n + 1)

If  then the value of  is

If  then the value of  is

• -1

• 3

• 1

• 1

If  then the value of  is

• -18

• 18

• 36

• 36

If  then the value of  is

• 9

• abc

• a+b+c

• a+b+c

If then the value of  is

• 4

• 52

• 64

• 64

If a, b, c are three non-zero real numbers such that a + b + c = 0, and  then the value of  is

• 3

• 2

• 0

• 0

If  and  then the value of ab is

• -1

• 0

• 2

• 2

If a = 25,  b = 15,  c = -10, then the value of 

• 30

• -15

• -30

• -30