(i) 49y^{2} + 84yz + 36z^{2 }

= (7y)^{2 }+ 2 × (7y) × (6z) + (6z)^{2}

= (7y + 6z)^{2} [(a + b)^{2} = a^{2} + 2ab + b^{2}]

(ii) 4x^{2} − 8x + 4

= (2x)^{2} − 2 (2x) (2) + (2)^{2}

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

= [(2) (x − 1)]^{2} = 4(x − 1)^{2}

(iii) 121b^{2} − 88bc + 16c^{2}

= (11b)^{2} − 2 (11b) (4c) + (4c)^{2}

= (11b − 4c)^{2} [(a − b)^{2} = a^{2} − 2ab + b^{2}]