the numbers a and b are negative in nature.the sign of which of te following expressions cannot be determined with certainty?

a.a+b

b.a-b

c.a*b

d.a divided by b

Answer:
We know our numbers a And b are in negative in sign , For checking uncertainty we replace a = -a  And b = - b in all options And observe uncertainty . As:
a ) a + b = ​​- a + (- b ) = - ( a + b)
So we can say that with certenity that ( a + b ) never be equal to - ( a + b)

b ) a - b = - a - ( - b) = - a + b , here we can't determine with certainty that final answer is positive or negative.
c ) a b = - a ( -b) = ab 

​d) $\frac{a}{b} = \frac{- a}{- b } \Rightarrow \frac{a}{b}$

So only in option B we ​can't be determined with certainty .    ( Ans)