Answer ক. (5p - 3q) (p + 7q)
আমরা জানি,
ab =` ((a + b)/2)^2 - ((a - b)/2)^2`
:. (5p - 3q) (p + 7q)
`= {((5p - 3q) + (p + 7q))/2}^2 - {((5p - 3q) - (p + 7q))/2}^2`
`= ((5p - 3q + p + 7q)/2)^2 - ((5p - 3q - p - 7q)/2)^2`
`= ((6p + 4q)/2)^2 - ((4p - 10q)/2)^2`
`= {(2(3p + 2q))/2}^2 - {(2(2p - 5q))/2}^2`
`= (3p + 2q)^2 - (2p - 5q)^2`
উত্তর: `(3p + 2q)^2 - (2p - 5q)^2`
খ.(6a + 9b) (7b - 8a)
আমরা জানি,
ab =` ((a + b)/2)^2 - ((a - b)/2)^2`
:. (6a + 9b) (7b - 8a)
= `{((6a + 9b) + (7b - 8a))/2)^2 - {((6a + 9b) - (7b - 8a))/2}^2`
= `((6a + 9b + 7b - 8a)/2)^2 - ((6a + 9b - 7b + 8a)/2)^2`
=` ((16b - 2a)/2)^2 - ((2b + 14a)/2)^2`
=` {(2(8b - a))/2}^2 - {(2(b + 7a))/2}^2`
=` (8b - a)^2 - (b + 7a)^2`
উত্তর: ` (8b - a)^2 - (b + 7a)^2`
গ. (3x + 5y) (7x - 5y)
আমরা জানি,
ab =` ((a + b)/2)^2 - ((a - b)/2)^2`
:. (3x + 5y) (7x - 5y)
=` {((3x + 5y) + (7x - 5y))/2}^2 - {((3x + 5y) - (7x - 5y))/2}^2`
=` ((3x + 5y + 7x - 5y)/2)^2 - ((3x + 5y - 7x + 5y)/2)^2`
=` ((10x)/2)^2 - ((- 4x + 10y)/2)^2`
=` (5x)^2 - {(- 2 (2x - 5y))/2}^2`
=` (5x)^2 - (2x - 5y)^2`
= `(5x)^2 - (2x - 5y)^2`
উত্তর: `(5x)^2 - (2x - 5y)^2`
ঘ. (5x + 13) (5x - 13)
আমরা জানি,
ab = `((a + b)/2)^2 - ((a - b)/2)^2`
:. (5x + 13) (5x - 13)
=` {((5x + 13) + (5x - 13))/2}^2 - {((5x + 13) - (5x - 13))/2}^2`
=` ((5x + 13 + 5x - 13)/2)^2 - ((5x + 13 - 5x + 13)/2)^2`
=` ((10x)/2)^2 - ((26)/2)^2`
= `(5x)^2 - (13)^2`
উত্তর: `(5x)^2 - (13)^2`