(i) (1.1m − 0.4) (1.1 m + 0.4)

= (1.1m)^{2} − (0.4)^{2} [(a + b) (a − b) = a^{2} − b^{2}]

= 1.21m^{2} − 0.16

(ii) (a^{2} + b^{2}) (− a^{2} + b^{2}) = (b^{2 }+ a^{2}) (b^{2} − a^{2})

= (b^{2})^{2} − (a^{2})^{2} [(a + b) (a − b) = a^{2} − b^{2}]

= b^{4 }− a^{4}

(iii) (6x − 7) (6x + 7) = (6x)^{2 }− (7)^{2} [(a + b) (a − b) = a^{2} − b^{2}]

= 36x^{2} − 49