Pl solve thirteenth question.

Dear Student ,

13 (i) x^{4} - y^{4} + x^{2} - y^{2} = {(x^{2})}^{2} - {(y^{2})}^{2} + x^{2} - y^{2} = (x^{2} + y^{2}) (x^{2} - y^{2}) + (x^{2} - y^{2}) = (x^{2} - y^{2}) (x^{2} + y^{2} + 1) = (x + y) (x - y) (x^{2} + y^{2} + 1) [using identity a^{2} - b^{2} = (a + b) (a - b)]

(ii) 64 a^{2} - 9 b^{2} + 42 bc - 49 c^{2} = {(8 a)}^{2} - [{(3 b)}^{2} - 2 \times 3 b \times 7 c + {(7 c)}^{2}] = {(8 a)}^{2} - {[3 b - 7 c]}^{2} [Using a^{2} - b^{2} = (a - b) (a + b)] = (8 a - 3 b + 7 c) (8 a + 3 b - 7 c) [using identity a^{2} - b^{2} = (a + b) (a - b), {(a + b)}^{2} = a^{2} + b^{2} + 2 ab, {(a - b)}^{2} = a^{2} + b^{2} - 2 ab]

Regards