(a) Here \(a>0\) \(\displaystyle\Rightarrow\) −a will be a negative number.

Thus, sign of -a is negative .

(b) It is known that product of two negative number will be positive.

As \(b<0\) and \(c<0\) \(\displaystyle\Rightarrow\) \(bc>0\).

Thus, sign of bc is positive.

(c) It is known that when a negative number is subtracted from a positive number, the resultant number will be positive.

Here \(a>0,b<0\) \(\displaystyle\Rightarrow\) \(a−b>0.\)

Thus, sign of a-b is positive.

(d) Here

\(a>0,b<0\) \(\displaystyle\Rightarrow\) \(ab<0\)

\(a>0,c<0\) \(\displaystyle\Rightarrow\) \(ac<0\)

So ac and bc negative.

It is known that sum of two negative number will be negative.

Thus, \(ab+ac<0.\)

Thus, sign of \(ab + ac\) is .