`9 xx (-13)-13`=____.

Verify each of the following: (i) (3)/(7)xx(-5)/(7) = (-5)/(9)xx(3)/(7) (ii) (8)/(7) xx (13)/(9) = (13)/(9) xx (-8)/(7) (iii) (-12)/(5)xx (7)/(-36) = (7)/(-36) xx (-12)/(5) (iv) -8 xx (-13)/(12) = (-13)/(12)xx(-8)

[(2/13)^(-6)-:(2/12)^(3)]^(3)xx(2/13)^(-9)= ______________

Solve:- (-13)^18 xx (-13)^12 = ?

Simplify : (-5)/(9) xx ((-10)/(13)) xx ((21)/(11)) xx (-7)

Simplify: (i) (-4/7) xx (21/20) , (ii) (-13)/9 xx (-21)/(-39)

9/10+(-13/8)

Evaluate the following (-9) xx (-13)

Find the sum 5 xx 7 +7xx9+ 9 xx 11 +11xx13+ 13 xx 15 + ……. upto n terms.

Compare the sums: 9 + (– 13) and –13 + 9.