Question

Show that:
${(4x + 7y)}^{2} - {(4x - 7y)}^{2} = 112xy$
send a correct answer quickly.​

Answer 1

x=7y(y+1)/8 or x=7y(y+1) by 8
This answer is correct :)

Answer 2

$(4x + 7y) {}^{2} = 4 {x}^{2} + 2 \times 4x × 7y + 7 {y}^{2} \\ \: \: \: \: \: \: \: \: \: \: \: \: \: = 16 {x}^{2} + 56xy + 49 {y}^{2}$

$(4x - 7y) {}^{2} = 4 {x}^{2} - 2 \times 4x \times 7y + 7 {y}^{2} \\ \: \: \: \: \: \: \: \: \: \: \: \: \: = 16 {x}^{2} - 56xy + 49 {y}^{2}$

$(4x + 7y) {}^{2} - (4x - 7y) {}^{2} \\ {16x }^{2} + 56xy + 49 {y}^{2} - (16 {x}^{2} - 56xy + 49 {y}^{2} ) \\ = 16x {}^{2} + 56xy + 49 {y}^{2} - 16 {x}^{2} + 56xy - 49 {y}^{2} \\ = 112xy$