` a.1 `
` (3 + xy^{2})^2 `
` = 3^{2} + 2.3.xy^{2} + (xy^{2})^2 `
` = 9 + 6xy^{2} + x^{2}y^{4} `
` a.2 `
` (10 - 2m^{n})^{2} `
` = 10^{2} - 2.10.2m^{n} + (2m^{n})^{2} `
` = 100 - 40m^{n} + 4m^{2n} `
` a.3 `
` = (a - b^{2})(a + b^{2}) `
` = a^{2} - (b^{2})^{2} `
` = a^{2} - b^{4} `