[tex]a. {(x + 4)}^{2} = {x}^{2} + 2 \times 4 \times x +16 = {x}^{2} + 8x + 16 \\ {(a + b)}^{2} = {a}^{2} + 2 \times a \times b + {b}^{2} \\
b. {(10 x - 5)}^{2} = 100 {x}^{2} - 2 \times 5 \times 10x + 25 = 100 {x}^{2} - 100x + 25 \\ {(a - b)}^{2} = {a}^{2} - 2 \times a \times b + {b}^{2} \\
c. {(2x + 3)}^{2} = 4 {x}^{2} + 12x + 9 \\ {(a + b)}^{2} = {a}^{2} + 2 \times a \times b + {b}^{2} \\
d. (r - x)(x + r) = {r}^{2} -16 \\ si \: ton \: x = b \: et \: r = a \: alors \: tu \: as \: x = \: 4\\ (a - b)(a + b) = {a}^{2} - {b}^{2} \\
e. (7x + 1)(7x - 1) = 49 {x}^{2} - 1 \\ (a + b)(a - b) = {a}^{2} - {b}^{2} [/tex]
